Download Section 1: ON THE MOVE

Standard Grade Physics
Section 1: ON THE MOVE
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R
U
Name: ________________________
Class: _____
Text and page layout copyright Martin Cunningham, 2005.
Majority of clipart copyright www.clipart.com, 2005.
"TRANSPORT"
Teacher: __________________
Section 1: ON THE MOVE
Why Use the Term "Average Speed"?
When an object moves over a large distance, its speed
rarely stays the same.
For example, a bus travelling from Glenrothes to
Kirkcaldy will change its speed many times during its
journey as it negotiates traffic and stops/starts to collect
and drop off passengers.
See you at
EAT
FRUIT
This is why we use the term average speed when
describing the movement of objects which travel a
large distance.
Even for objects which only travel a short distance (like a
radio-controlled toy car), we still use the term
average speed because the speed will change,
even over the short distance travelled.
Average Speed Calculations
The average speed ( v ) of a moving object is the
distance it travels in a given time.
1) Calculate the missing quantity in each case:
average speed = ?
average speed = ?
average speed = ?
average speed = ?
distance = 500 metres
distance = 15 000 metres
distance = 10 metres
distance = 45 metres
time = 5 seconds
time = 25 seconds
time = 0.5 seconds
time = 2.5 seconds
average speed = ?
average speed = ?
average speed = ?
average speed = ?
distance = 59.5 metres
distance = 1 440 metres
distance = 750 metres
distance = 540 metres
time = 3.5 seconds
time = 80 seconds
time = 500 seconds
time = 12 seconds
average speed = 12 metres per second
average speed = 0.001 metres per second
average speed = 1.2 metres per second
average speed = 10.2 metres per second
distance = ?
distance = ?
distance = 6 metres
distance = 100 metres
time = 6 seconds
time = 120 seconds
time = ?
time = ?
For very long journeys of kilometres/miles which take hours to complete, average speeds are quoted in units of
kilometres per hour (km/h) or miles per hour (mph).
You may have to solve problems involving these units in tests or in your Standard Grade Physics exam.
2) Convert the following speeds
from kilometres per hour to
metres per second.
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)-.
-.
3) Wendy takes 45 minutes
to run a 10 kilometre race.
(a) What is Wendy's time in
hours (expressed as a
decimal)?
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5) The Eurostar train
service from London
to Brussels takes
2 hours 45 minutes
to cover the
340 kilometre track distance.
Calculate the average speed of the
train in kilometres per hour.
(b) Calculate Wendy's average
speed in kilometres per hour.
7) An extract from
an express coach
timetable is
shown below.
Assuming the coach departs and
arrives exactly on time, calculate
the total distance travelled in
kilometres if the average speed
for the journey is
80 kilometres per hour.
(a) 18 kilometres per hour.
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(b) 72 kilometres per hour.
4) A cruise ship
takes a time of
5 hours 30 minutes
to sail 33 miles.
(a) Express the time in hours
in decimal form.
(c) 100 kilometres per hour.
(b) Calculate the average speed of
the ship in miles per hour.
6)
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Using information from these
timetable extracts, calculate the
train's average speed in
miles per hour.
#
8) A coach travels
the 157.5 mile
road distance
from Edinburgh to
Inverness at an average speed of
45 miles per hour.
Calculate the time taken for the
journey in hours.
Measuring Average Speed: Human Timing
To measure the average speed ( v ) of a moving object (for example, a
radio-controlled toy car), we can use a measuring tape and stopwatch:
9) The following readings were obtained during
3 runs of the radio-controlled car.
For each set of readings, calculate the
average speed of the radio-controlled car:
Run 1
distance travelled (d) = 9 metres
time taken (t) = 1.8 seconds
*
1) With a m _ _ _ _ _ _ _ _ t _ _ _ , measure (and mark with chalk)
a distance of several metres on the ground.
2) With a s _ _ _ _ _ _ _ _ , time how long it takes the radio-controlled
toy car to travel this distance.
3) Calculate the average speed of the toy car using the formula:
Run 2
distance travelled (d) = 12 metres
time taken (t) = 2.5 seconds
""
,
*
" '
Run 3
/ " "
distance travelled (d) = 15 metres
time taken (t) = 6.0 seconds
%'
(
%
#
%)
.
%
Measuring Average Speed: Electronic Timing
Stopwatches and Human Reaction Time
Using a stopwatch to time moving objects does not give us a
very accurate value for the time taken. This is due to
human reaction time.
For example, imagine you are timing a radio-controlled toy car
from the moment it starts to the moment it has travelled
5 metres. When your eyes see the car start to move, they send
a message to your brain. Your brain processes this message
then sends another message to your finger telling it to press
the start button on the stopwatch - but it takes a fraction of a
second for all this to happen, so the car is already moving
before the start button is pressed. When the car reaches the
5 metre mark, the same signalling/reaction process takes place
in your body - the car will have travelled past the 5 metre
mark before the stop button is pressed. Because of this, the
timing of the car journey is not accurate.
This is particularly important when timing sprint races where a
difference of less than 0.001 seconds can mean the difference
between first and second place! In cases like this,
electronic timing is used - This does not involve humans
pressing buttons (no human reaction time) so is far
more accurate than human timing.
To measure the average speed ( v ) of a moving object (for
example, a trolley rolling down a slope) with electronic
timing, we use a measuring tape and 2 light gates
connected to an electronic timer. A mask (thick card) is
fixed on top of the trolley.
*
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!
(
"
2.135 s
"
When the mask breaks the light beam of the top light gate,
the electronic timer is automatically switched on.
When the mask breaks the light beam of the bottom light
gate, the electronic timer is automatically switched off.
The electronic timer shows the time the trolley takes to travel
from the top light gate to the bottom light gate.
1) With a m _ _ _ _ _ _ _ _ t _ _ _ , measure the distance between the
2 light gates.
2) Put the trolley at the top of the slope and let it run down the slope
(so that the mask passes through the l _ _ _ _ b _ _ _ of both
l _ _ _ _ g _ _ _ _ ).
3) Read the time taken for the trolley to travel from the top light gate to the
bottom light gate from the e _ _ _ _ _ _ _ _ _ t _ _ _ _ .
3) Calculate the average speed of the trolley using the formula:
10) The following readings were obtained during
3 separate runs of the trolley down the slope.
For each set of readings, calculate the
average speed of the trolley as it ran down the
slope:
Run 1
distance travelled (d) between light gates =
1.25 metres
time taken (t) to travel between light gates =
0.250 seconds
""
,
*
" '
Run 2
/ " "
*
*
(
distance travelled (d) between light gates =
0.80 metres
% +#
% #
time taken (t) to travel between light gates =
0.500 seconds
%)
Run 3
0%
%
0 %
distance travelled (d) between light gates =
1.50 metres
time taken (t) to travel between light gates =
0.750 seconds
Instantaneous Speed
The instantaneous speed (v) of a moving object is its speed at a
particular instant of time.
The instantaneous speed of a car is shown
on its speedometer.
As the instantaneous speed of the car
changes, the speedometer reading changes.
Measuring Instantaneous
Speed: Electronic Timing
To measure the instantaneous speed (v) of
a moving object (for example, a trolley rolling
down a slope) at a particular point on the
slope, we employ electronic timing - 1 light
gate is connected to an electronic timer.
A short mask (about a 1 or 2 cm length of
thick card) is fixed on top of the trolley.
*
!
!
(
The instantaneous speed of a moving object is estimated by measuring the
distance the object travels in a very short time - Much less than 1 second.
The smaller the measured time, the better will be the estimate for the object's
instantaneous speed.
For times longer than about 0.005 seconds, the speed determined is really the
average speed.
The method used to measure the time of travel has an effect on the estimated
value for instantaneous speed.
A stopwatch
cannot be used
because we are
not able to press
the start and stop
buttons quickly
enough - Slow
human reaction
time.
We have to use
electronic
timing which
can measure
very small time
intervals - For
example,
0.001
seconds.
0.001 s
"
"
0.001 s
When the front edge of the mask enters the
light beam of the light gate, the electronic timer is
automatically switched on.
When the back edge of the mask leaves the
light beam of the light gate, the electronic timer is
automatically switched off.
The electronic timer shows the time the mask takes to
travel through the light gate.
1) With a r _ _ _ _ , measure the l _ _ _ _ _ of the short mask.
2) Place the l _ _ _ _ g _ _ _ at the particular point on the slope where you
want to measure the trolley's i _ _ _ _ _ _ _ _ _ _ _ _ speed.
3) Put the trolley at the top of the slope and let it run down the slope (so that the
short mask passes through the l _ _ _ _ b _ _ _ of the l _ _ _ _ g _ _ _.)
3) Calculate the instantaneous speed of the trolley using the formula:
"
,
,
,
"
"
11) The following readings were obtained during
3 separate runs of the trolley down the slope.
For each set of readings, calculate the
instantaneous speed of the trolley as it passed
through the light gate:
Run 1
distance (length of mask) = 0.01 metres.
time taken (t) for mask to travel through
light gate = 0.001 seconds.
Run 2
*
" '
,
(
,
distance (length of mask) = 0.015 metres.
/ " "
time taken (t) for mask to travel through
light gate = 0.003 seconds.
( %
(
%
+
%)
Run 3
distance (length of mask) = 0.02 metres.
time taken (t) for mask to travel through
light gate = 0.005 seconds.
0
%
Comparing Instantaneous and Average Speeds
In most cases, at any
particular instant of time, the
instantaneous speed of a
moving object will have a
different value from its
average speed - because
most objects speed up and
slow down during their
journey.
The instantaneous and
average speeds will only have
the same value over a long
period of time if the object:
does not move.
does not speed up or
slow down.
12) (a) Why do we use the term average speed to describe the movement of objects which travel a
large distance? ___________________________________________________________________
_______________________________________________________________________________
(b) Describe and explain the movement of a bus on a typical journey from Glenrothes to Kirkcaldy:
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
13) (a) What do we mean by the instantaneous speed of an object? _________________________
_______________________________________________________________________________
(b) What device in a car shows the instantaneous speed of the car? ________________________
(c) Explain whether we can use a stopwatch to determine the instantaneous speed of an object:
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
(d) Why is electronic timing used to determine the instantaneous speed of an object?
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
14) (a) In most cases, at any particular moment in time, does the instantaneous speed of an object
have the same or a different value from its average speed? ___________________
(b) Explain why: __________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
(c) Give 2 examples of when the instantaneous and average speeds of an object have the same
value: __________________________________________________________________________
_______________________________________________________________________________
Acceleration (and Deceleration)
This diagram shows a motorbike accelerating from a
stationary start (rest, 0 metres per second).
0
#
#
After each second:
Its instantaneous speed has increased.
It has travelled further than it travelled the second before.
+#
This diagram shows a motorbike decelerating from an
instantaneous speed of 15 metres per second to
rest (0 metres per second).
-#
0
#
#
After each second:
Its instantaneous speed has decreased.
It has travelled less far than it travelled the second before.
+#
-#
When an object's instantaneous speed increases with time, the object is a _ _ _ _ _ _ _ _ _ _ _.
When an object's instantaneous speed decreases with time, the object is d _ _ _ _ _ _ _ _ _ _ _.
The acceleration (a) or deceleration of an object is its
change in instantaneous speed over a given time.
"
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∆
,
"
"
+
Acceleration Calculations
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,
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15) In each case, calculate the acceleration of the vehicle:
(a) Farmer
Jones' tractor
starts from
rest and
speeds up to
8 metres per
second in
10 seconds.
(b) In their
go-kart, Jill
and her Mum
speed up from
rest to
6 metres per second in
12 seconds.
(c) In their golf
cart, Tom and
Sue speed up
from 2 metres per
second to
9 metres per second in
5 seconds.
∆
%
1
∆
∆
∆
%
0
(d) On her motor (e) Sid's sleigh
scooter, Milly takes
takes
5 seconds to speed 20 seconds to
up from 3 metres speed up from
per second to 13
4 metres per second to
metres per second.
12 metres per second.
(f) Mike's
motorbike
takes
5 seconds to
speed up from 10 metres per
second to 30 metres per
second.
16) Barah's
forklift truck
accelerates at
0.25 metres per
second per
second while
speeding up from rest to
5 metres per second.
Calculate the time this takes.
More Acceleration Calculations
17) Sam
somersaults
across a gym
floor. He starts
from rest and
speeds up to
2.4 metres per second, having
accelerated at 0.3 metres per
second per second.
∆
can also be written in the form
"
"
What time does this take?
"
"
+
*
18) Starting
from rest, a
cheetah
accelerates at
3.6 metres per second per
second for 7.5 seconds.
Calculate the Cheetah's
change in speed during this
time.
19) Starting
from rest, a
red kangaroo
accelerates
at 3 metres
per second per second for
5.5 seconds.
By how much does the
kangaroo's speed increase
over this time?
" / " "
"
"
,
"
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2
*
-
,
,
2
-
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*
2
2
,
,
, -
2
2
$
2
0
1
1
$
.
-
0
%
2
0
0
2
0
The - sign indicates
"deceleration"
20) In each case: (a) Calculate the acceleration or deceleration over the stated time interval. (b) Tick the correct acceleration or deceleration box.
initial speed (u) = 0 m/s
initial speed (u) = 0 m/s
initial speed (u) = 4.5 m/s
initial speed (u) = 3.6 m/s
final speed (v) = 6 m/s
final speed (v) = 3 m/s
final speed (v) = 0 m/s
final speed (v) = 0 m/s
time = 12 s
time = 2 s
time = 2.5 s
time = 6 s
initial speed (u) = 1.5 m/s
initial speed (u) = 7.8 m/s
initial speed (u) = 5.5 m/s
initial speed (u) = 0.6 m/s
final speed (v) = 7.5 m/s
final speed (v) = 2.3 m/s
final speed (v) = 2.3 m/s
final speed (v) = 6.8 m/s
time = 2 s
time = 2.5 s
time = 8 s
time = 4.1 s
initial speed (u) = 12.3 m/s
initial speed (u) = 0.5 m/s
initial speed (u) = 0.9 m/s
initial speed (u) = 6.7 m/s
final speed (v) = 1.5 m/s
final speed (v) = 2.5 m/s
final speed (v) = 2.1 m/s
final speed (v) = 2.3 m/s
time = 9 s
time = 20 s
time = 6 s
time = 5.5 s
21) As a
bobsleigh
reaches a
steep part of
track, its
speed
increases
from 24 m/s to 36 m/s.
This happens in 0.4 s.
22) An arrow hits
a stationary
target at 50 m/s
and comes to
rest in 0.1 s.
Calculate the
deceleration of the arrow once it
hits the target.
23) Starting from rest, a
fireman slides down a
pole with an
acceleration of 1.2 m/s2.
His speed at the bottom
of the pole is 3.6 m/s.
24) A bee,
decelerating
at 0.7 m/s2,
slows down
from 6.7 m/s
to 2.5 m/s.
Calculate the time taken
to slide down the pole.
What time
does this
take?
Calculate the acceleration of the
bobsleigh during this time.
25) When a
stationary rugby
ball is kicked, it
is in contact with
a player's boot
for 0.05 s. During this short time,
the ball accelerates at 600 m/s2.
Calculate the speed at which the
ball leaves the player's boot.
26) A helicopter
is flying at
35 m/s. It then
decelerates at
2.5 m/s2 for 12 s.
Calculate the
speed of the helicopter after the
12 s.
27) A speed of a
conveyor belt is
increased to
2.8 m/s by
accelerating it at
0.3 m/s2 for 4 s.
Calculate the
initial speed of the conveyor belt.
28) A van
decelerates at
1.4 m/s2 for 5 s.
This reduces its
speed to 24 m/s.
Calculate the van's initial speed.
Car Performance
Car manufacturers provide performance information for each model
they produce, so that customers can compare how the cars perform.
29) In each case, calculate the acceleration of the car in
kilometres per hour per second and in miles per hour per second:
One performance figure always provided is the time a car takes to
accelerate from rest (0 kilometres or 0 miles per hour) to a speed of
100 kilometres per hour = 62 miles per hour.
/
,
0
1
!
/
(
(
!"
,"
'+
2
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,"
"
"
1
1
!
, 2
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"
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3
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, 2
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, 2
) *
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0%
30) (a) Arrange the 4 cars
1) ____________________ (greatest acceleration) (b) By just looking at the time a car takes to speed up
shown on these 2 pages
from rest to 100 km/h or 62 mph, how can you tell
2) ____________________
(16 + 17) in order of their
whether the car has a small or large acceleration?
3)
____________________
acceleration performance:
____________________________________________
____________________________________________
4) ____________________ (least acceleration)
____________________________________________
Speed-Time Graphs
The motion of any object can be represented by a line drawn on a speed-time graph:
"#
2
#
"
)
2
"
speed/ metres per second
speed/ metres per second
31) Describe the motion represented by the line on each speed-time graph:
10
9
8
7
6
5
4
3
2
50
45
40
35
30
25
20
15
10
5
1
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
0 - 10 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
0 - 8 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
10 - 15 seconds: __________ _________ of ____ metres per second.
8 - 11 seconds: __________ _________ of ____ metres per second.
15 - 20 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
11 - 18 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
speed/ metres per second
speed/ metres per second
10
9
8
7
6
5
4
3
2
1
0
50
45
40
35
30
25
20
15
10
5
1
2
3
4
5
6
7
8
0
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
time/ seconds
0 - 10 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
0 - 30 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
10 - 14 seconds: __________ _________ of ____ metres per second.
30 - 75 seconds: __________ _________ of ____ metres per second.
14 - 20 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
75 - 100 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
speed/ metres per second
speed/ metres per second
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
50
45
40
35
30
25
20
15
10
5
0
100
90
80
70
60
50
40
30
20
10
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
0 - 5 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
time/ seconds
0 - 25 seconds: __________ _________ of ____ metres per second.
5 - 12 seconds: __________ _________ of ____ metres per second.
25 - 75 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
12 - 17 seconds: ___________ ____ from ____ metres per second
to ____ metres per second. (Constant/uniform _______________ ).
75 - 100 seconds: ___________ _______ from ____ metres per second
to ____ metres per second. (Constant/uniform _________________ ).
0 - 5 seconds: Speeding up from rest (0 metres per second) to
10 metres per second. (Constant/uniform acceleration).
0 - 30 seconds: Speeding up from 25 metres per second to
40 metres per second. (Constant/uniform acceleration).
5 - 15 seconds: Steady speed of 10 metres per second.
30 - 60 seconds: Steady speed of 40 metres per second.
15 - 20 seconds: Slowing down from 10 metres per second to
rest (0 metres per second). (Constant/uniform deceleration).
60 - 90 seconds: Slowing down from 40 metres per second to
rest (0 metres per second). (Constant/uniform deceleration).
10
9
8
7
6
5
4
3
speed/ metres per second
speed/ metres per second
32) Draw the line on each speed-time graph to represent the motion described:
50
45
40
35
30
25
20
15
2
10
1
5
0
1
2
3
4
5
6
7
8
0
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
time/ seconds
A helicopter, initially travelling at 80 metres per second, decelerates
constantly/uniformly to a speed of 60 metres per second in 25 seconds.
For the next 50 seconds, it continues to travel at this steady speed before
decelerating constantly/uniformly to rest in a further 25 seconds.
speed/ metres per second
speed/ metres per second
With uniform/constant acceleration, a motorcycle takes 8 seconds to
speed up from rest to 20 metres per second. The motorcycle continues to
travel at this steady speed for 4 seconds. It then increases its speed to
45 metres per second (constant/uniform acceleration) in 7 seconds.
50
45
40
35
30
25
20
15
10
100
90
80
70
60
50
40
30
20
5
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
10
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
time/ seconds
Calculating Acceleration
(or Deceleration) From a
Speed-Time Graph
Put numbers on each axis.
A cyclist travels at a steady speed of 9 metres per second for 6 seconds
before decelerating constantly/uniformly to a speed of 2 metres per
second in 7 seconds. She then travels at this steady speed for a further
5 seconds.
By taking speed and time values from a
speed-time graph, we can calculate the acceleration or
deceleration of the object which the graph represents.
(
&5
/
"
speed/ metres per second
speed/ metres per second
Maximum speed = 9 metres per second. Total time = 18 seconds.
∆
%
time/ seconds
%
Put numbers on each axis.
Maximum speed = 90 metres per second. Total time = 20 seconds.
speed/ metres per second
A racing car travels at a steady speed of 10 metres per second for
2 seconds before accelerating constantly/uniformly for 12 seconds to a
speed of 90 metres per second. The car then immediately decelerates
constantly/uniformly for 6 seconds to a speed of 70 metres per second.
50
45
40
35
30
25
20
15
10
5
0
∆
1
2
3
4
5
4
4
∆
4
time/ seconds
%
7
8
9 10
time/ seconds
∆
"
6
speed/ metres per second
speed/ metres per second
33) Calculate the acceleration represented by the line on each speed-time graph.
10
9
8
7
6
5
4
3
2
1
0
50
45
40
35
30
25
20
15
10
5
1
2
3
4
5
6
7
8
0
9 10 11 12 13 14 15 16 17 18 19 20
50
45
40
35
30
25
20
15
10
5
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
time/ seconds
speed/ metres per second
speed/ metres per second
time/ seconds
100
90
80
70
60
50
40
30
20
10
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
time/ seconds
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
time/ seconds
Calculating Distance Gone From a
Speed-Time Graph
The area under a speed-time graph representing the
motion of an object gives the distance gone by the object.
Distance and Acceleration Calculations
34) Each of the following speed-time graphs represent the motion
of a vehicle.
For each graph, calculate any accelerations and decelerations of
the vehicle, plus the distance gone:
"
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speed/ m/s
speed/ m/s
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7
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3
3
2
2
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2
3
4
5
6
7
8
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5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
9 10 11 12 13 14 15 16 17 18 19 20
time/ s
time/ s
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5
20 5
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speed/ m/s
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7
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5
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3
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2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
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5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
time/ s
time/ s
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speed/ m/s
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50
45
40
35
40
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30
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20
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3
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7
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Standard Grade Physics
Section 2: FORCES AT WORK
Name: ________________________
Class: _____
Text and page layout copyright Martin Cunningham, 2005.
Majority of clipart copyright www.clipart.com, 2005.
"TRANSPORT"
Teacher: __________________
Section 2: FORCES AT WORK
Forces and Their Effects
The Force of Friction
A force can be thought of as a p _ _ _ or p _ _ _
on an object.
No surface is perfectly smooth.
Every surface has rough, uneven parts.
A force can change an object's:
When we move one surface over another,
the rough, uneven parts rub together.
s____
s____
d _ _ _ _ _ _ _ _ of travel
This creates a force which tries to slow down or stop the
movement.
This force is called friction.
The smoother the surfaces rubbing together, the
l _ _ _ _ the friction - Movement is e _ _ _ _ _.
The rougher the surfaces rubbing together, the
h _ _ _ _ _ the friction - Movement is
more d _ _ _ _ _ _ _ _.
Increasing and Decreasing Friction
The force of friction plays a vital part in our everyday lives - Sometimes we
need to increase it, other times we need to decrease it.
1) These diagrams show "friction in everyday life".
In each case, tick the correct box to show whether friction is being increased or decreased.
Write a brief note to explain the situation:
increased friction
increased friction
increased friction
decreased friction
decreased friction
decreased friction
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
increased friction
increased friction
increased friction
decreased friction
decreased friction
decreased friction
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
Air Friction/Resistance
and Streamlining
When an object moves through the air,
the air rubs against the object,
slowing it down.
This effect is known as air f _ _ _ _ _ _ _
or air r _ _ _ _ _ _ _ _ _.
2) Explain how a parachute works:
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
_____________________________
3) (a) What is meant by "streamlining" an
object? _______________________________
_____________________________________
_____________________________________
(b) Draw lines to represent the air flow over
these 2 cars :
(b) Explain
which car is
most
"streamlined":
_____________
_____________
_____________
_____________
_____________
_____________
_____________
_____________
Measuring Force
Force is measured in units called
n _ _ _ _ _ _ (symbol __ ).
We can measure force using a Newton balance.
4) (a) Label the diagram of a Newton balance using the words
in the word bank:
,
"
"
(b) Explain how a Newton balance
works: _______________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
(c) Explain how you would use a Newton balance to measure the
force required to pull open a drawer: _______________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
Mass and Weight
Mass
The mass of an object is the amount of material
in the object.
The unit of mass is the k _ _ _ _ _ _ _ ( _ _ ).
Weight
All objects attract (pull one another together) - This
attraction (pull) is known as the force of g _ _ _ _ _ _.
Weight is a force. It is the Earth's gravitational pull
on an object.
The unit of weight is the n _ _ _ _ _ ( __ ).
The force of gravity pulls every
object near or on the Earth's
surface down towards the centre of
the Earth with a force of
10 newtons for every kilogram
of mass.
This downwards force (weight)
per kilogram of mass is called the
g____________ f____
s _ _ _ _ _ _ _. (Symbol __ ).
Near the Earth's surface,
g = ___ newtons per kilogram
(N/kg).
5) When an object is hung
from a Newton balance,
what quantity does the
force reading on the
Newton balance
represent?
6) Each person is standing on a set of scales on the Earth's surface.
Calculate the weight of each person:
______________________
______________________
Mass and Weight
Calculations
Harry
(mass 80 kilograms)
Mary
(mass 55 kilograms)
David
Bertha
(mass 62 kilograms) (mass 110 kilograms)
For any object:
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7) Each weightlifter is working out in a gym on the Earth's surface.
Calculate the mass being lifted by each weightlifter:
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Dwayne
(lifting 1 000 newtons)
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Sonya
(lifting 150 newtons)
Tanya
Victor
(lifting 320 newtons) (lifting 1 600 newtons)
Balanced and Unbalanced Forces
We can show the direction of a force using an arrow.
8) In each case, calculate the size of the resultant force and state
any direction. Tick the correct box to show whether the forces acting
on the object are balanced or unbalanced.
Balanced Forces
#
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If the forces acting on an object are equal in size but
act in opposite directions, the forces are said to be
b _ _ _ _ _ _ _.
For
example:
%
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The forces cancel out.
They are equivalent to no force at all.
We say: 9
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balanced forces
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balanced forces
If the forces acting on an object are not equal in size,
the forces are said to be u _ _ _ _ _ _ _ _ _.
For
example: 0
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balanced forces
0
0
unbalanced forces
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Unbalanced Forces
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unbalanced forces
0
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unbalanced forces
balanced forces
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unbalanced forces
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The forces do not cancel out.
We could replace the forces with one force
(called a resultant force) which would have exactly the
same affect on the object.
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For the forces shown in the diagram above, we can say:
9
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unbalanced forces
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balanced forces
unbalanced forces
balanced forces
unbalanced forces
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balanced forces
unbalanced forces
Newton's First Law of Motion
If the forces acting on an object are
balanced (or no forces act), the
object's speed remains the same.
The object:
remains s _ _ _ _ _ _ _ _ _
continues to move at c _ _ _ _ _ _ _
s _ _ _ _ in a s _ _ _ _ _ _ _ l _ _ _.
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If the forces acting on an object are
unbalanced, the object:
a _ _ _ _ _ _ _ _ _ _ in the direction of the
u _ _ _ _ _ _ _ _ _ f _ _ _ _.
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For example:
The diagram shows the forces
which act on a car in the
horizontal direction:
9) The diagram shows the horizontal
forces acting on a motorbike during a
race.
How does the size of these forces
compare:
(a) Just before the start of the race when the motorbike is not
moving? _____________________________________________
_____________________________________________________
(b) One second after the start of the race when the motorbike is
accelerating forwards? _________________________________
_____________________________________________________
(c) A few seconds later when the motorbike has reached a
constant (terminal) speed? ______________________________
_____________________________________________________
(d) Just before the end of the race when the motorbike is
decelerating? _________________________________________
_____________________________________________________
10) The vertical forces acting on a skydiver are shown in the diagram.
2
The car is stationary at a set of traffic lights.
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________________________________
________________________________
________________________________
________________________________
________________________________
As the traffic lights change to green, the car accelerates forwards.
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After a few seconds, the car reaches a constant speed
(known as its t _ _ _ _ _ _ _ speed).
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(a) As soon as the skydiver jumps from
an aeroplane, he accelerates
downwards. Explain why:
,
,
(b) After a few seconds, the skydiver reaches a
constant (terminal) speed. Explain why:
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
Seat Belts
Seat belts are a vital safety feature in road vehicles.
Every year, thousands of people's lives are saved
because, during a vehicle crash, they were wearing a
seat belt.
Newton's Second Law of Motion
An object accelerates (or decelerates) when an
unbalanced force acts on it.
The acceleration of the object depend on the mass of
the object and the size of the unbalanced force acting
on it.
If you increase the mass of the object,
the acceleration ___________.
If you increase the size of the unbalanced force,
the acceleration ___________.
Acceleration, unbalanced force and mass are related
by the formula:
"
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Explain, in terms of forces, how a seat belt works:
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
_________________________________________________
5
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F = ma Calculations
11) Calculate
the
acceleration of
a car of mass
1 500 kilograms which is acted
upon by an unbalanced force of
4 500 newtons.
14) Daisy the diver has a
mass of 50 kilograms.
After jumping from a
diving board, she
accelerates downwards
towards a swimming pool at 10
metres per second per second.
Calculate the unbalanced force
acting on her.
17) Sally the snow
boarder accelerates
at 0.5 metres per
second per second
when an unbalanced
force of 30 newtons acts on her.
Calculate the combined mass of
Sally and her snow board.
20) A balloon of mass
0.001 kilograms
accelerates upwards
when acted upon by an
unbalanced force of
0.002 newtons. Calculate the
acceleration of the balloon.
12) A tractor and its
driver have a
combined mass of
1 700 kilograms. An
unbalanced force of
2 040 newtons drives the tractor
forward. Calculate the tractor's
acceleration.
15) Calculate the
unbalanced force
acting on a rocket of
mass 5 000 kilograms if
it accelerates upwards
from the ground at
0.8 metres per second per second.
18) When an
unbalanced force of
780 newtons acts on a
skydiver, he
accelerates towards the ground at
10 metres per second per second.
Calculate the mass of the skydiver
and his equipment.
21) A 10 000 kilogram
truck accelerates at
0.2 metres per second
per second. Calculate
the size of the unbalanced force
acting on the truck.
16) A minibus of mass
2 500 kilograms
accelerates at 0.75
metres per second per
second. Calculate the
unbalanced force acting on the
minibus.
19) A speed skater
accelerates at 1.5 metres
per second per second
when an unbalanced force
of 96 newtons acts on him.
Calculate the mass of the
speed skater.
13) An unbalanced
force of 91 newtons
acts on Simon and his
skateboard which have
a combined mass of
65 kilograms. Calculate the
acceleration of Simon and his
skateboard.
STOP
22) A mini hovercraft
accelerates at 1.6
metres per second per
second when an
unbalanced force of 1 840
newtons acts on it. Calculate the
mass of the hovercraft.
More F = ma Calculations
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23) In each case, determine:
(a) the size and direction of the unbalanced force acting on the object;
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(b) the size and direction of the object's acceleration.
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Standard Grade Physics
Section 3: MOVEMENT MEANS ENERGY
Name: ________________________
Class: _____
Text and page layout copyright Martin Cunningham, 2005.
Majority of clipart copyright www.clipart.com, 2005.
"TRANSPORT"
Teacher: __________________
Section 3: MOVEMENT MEANS ENERGY
Work Done = Energy Transferred
Energy Transformations (Changes)
For a Moving Vehicle
When a force moves an object through a distance,
the force does work on the object:
As a vehicle moves from one place to another, different
energy transformations (changes) take place.
1) Complete the table to show the energy transformations
(changes) taking place for each type of vehicle motion:
Type of
Vehicle Motion
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Energy
Transformation(s)
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The work done by the force on the object leads to a
transfer of energy.
One form of energy is transformed (changed) to
other forms of energy.
#
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EW = Fd Calculations
2) Calculate the
work done by
Matthew when he
pulls a barrow full of
sand with a
constant force of 2 000 newtons
over a distance of 15 metres.
5) Calculate the
energy transferred by
Tony when he pushes
his luggage 30 metres
with a constant force of
230 newtons.
8) A horse does
75 000 joules of
work by pulling a
cart 25 metres with
a constant force. Calculate the size
of the force applied by the horse.
11) Sean pushes
Stefan in his
go-kart with a
constant force of
700 newtons,
doing 5 600 joules of work.
Calculate the distance travelled.
3) Charlene pushes
her baby cousin's
pram 50 metres
along the road by
applying a constant
force of 200 newtons.
Calculate the work done.
6) Calculate the
energy transferred by
Lee when he pulls a
rickshaw 200 metres
with a constant force
of 1 200 newtons.
9) When Rianne pushes
a wheelbarrow
12 metres with a
constant force, she does
13 800 joules of work.
Calculate the size of the force
applied by Rianne.
12) Darren does
3 870 joules of work
when he pulls his golf
trolley with a constant
force of 215 newtons.
Calculate the distance Darren
pulls the trolley.
7) How much energy is
transferred by Michael
when he pushes his
car 15 metres with a
constant force of
1 500 newtons.
10) A car pulls a
trailer 500 metres
along the road with
a constant force. The car transfers
1 800 000 joules of energy.
Calculate the size of the force
applied.
4) In order to pull
a sledge
75 metres across
the snow, a dog
must exert a constant force of
1 000 newtons. How much work
must the dog do?
13) A horse transfers
360 000 joules of
energy when it pulls a
plough with a constant
force of 4 000 newtons. Calculate
the length of the furrow produced.
Gravitational Potential Energy
Any object which is above the ground has
gravitational potential energy.
"
"
5
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"
)
EP = mgh Calculations
14) Calculate the gravitational
potential energy of a
15 kilogram cheese which is
sitting on a 1.5 metre high shelf.
&
5
16) A star (mass
0.75 kilograms) sits on top of a
12 metre high Christmas tree.
Calculate the gravitational
potential energy of the star.
"
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When an object is lifted up off the
ground, work is done against gravity
- The work done is equal to the
i _ _ _ _ _ _ _ in the object's
gravitational potential energy.
When an object is lowered down
towards the ground, work is done by
gravity - The work done is equal to the
d _ _ _ _ _ _ _ in the object's
gravitational potential energy.
15) 'Hoot' the
owl has a mass
of 2.8 kilograms.
Calculate her
gravitational
potential
energy when
she is sitting
9.5 metres up a
tree.
17) Calculate the
gravitational
potential energy
of Graham's golf
ball (mass
0.045 kilograms)
which is stuck
1.8 metres up a tree.
18) When Boris
holds a set of
weights
1.9 metres above
the floor, the
weights have a
gravitational
potential energy of 3 800 joules.
Calculate the mass of these
weights.
19) During a 'strong
man' competition,
Hamish holds a
150 kilogram boulder
above the ground.
If the boulder has a
gravitational potential
energy of 1 650 joules,
calculate its height above the
ground.
20) Kayleigh
has a mass of
62 kilograms.
She climbs
2.5 metres up
a ladder.
Determine:
22) A
helicopter
(mass 6 200
kilograms)
increases its height above the
ground by 115 metres.
Determine:
(a) Kayleigh's increase in
gravitational potential energy;
(a) the increase in gravitational
potential energy;
(b) the work done against
gravity.
(b) the work done against
gravity.
21) Ally the
abseiler
descends
35 metres down a
rope. His mass is
70 kilograms.
Determine:
(a) Ally's decrease in
gravitational potential energy;
(b) the work done by gravity.
23) A skydiver (mass
68 kilograms) falls
350 metres through
the air.
Determine:
(a) the decrease in gravitational
potential energy;
(b) the work done by gravity.
24) When Alana
climbs 8.5 metres
up a rope, she does
4 675 joules of work
against gravity.
Determine Alana's
mass.
25) When Shona,
mass 66 kilograms,
dives from a high
board into a
swimming pool,
16 500 joules of
work is done by
gravity. Determine the distance
Shona falls through.
Kinetic Energy
EK = 1/2 mv2 Calculations
Kinetic energy is movement energy.
A moving object's kinetic energy depends on its
mass and speed:
The greater the mass of a moving object,
the ___________ is the value of its kinetic energy.
The greater the speed of a moving object,
the ___________ is the value of its kinetic energy.
26) Quasim, who
has a mass of
60 kg, is jogging at
a speed of 5 m/s.
Calculate Quasim's
kinetic energy.
28) Kevin's kite
has a mass of
0.02 kg. It is
travelling
through the air
with a speed of 3 m/s. Calculate
the kinetic energy of the kite.
Kinetic energy, mass and speed
are related by the formula:
,
)
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27) Calculate the kinetic energy
of a 0.12 kg arrow which is
travelling through the air with a
speed of 50 m/s.
29) Ryan throws a
paper aeroplane
of mass 0.001 kg.
The plane leaves
his hand with a
speed of 5 m/s.
Calculate the kinetic energy of
the plane at this instant.
30) Dominique
has a mass of
55 kg. During
her
gymnastics
display, she
springs off the
end of a beam
with a speed of 4 m/s.
Calculate the kinetic energy of
Dominique at this instant.
31) Ross fires
a 0.002 kg
stone from a
catapult. If the
stone leaves
the catapult
with a speed of
10 m/s,
calculate the kinetic energy of
the stone at this instant.
32) A bullet, travelling through the
air with a speed of 1 200 m/s, has
11 520 J of kinetic energy.
Calculate the mass of the bullet.
33) Duncan (mass 64 kg) has 72 J
of kinetic energy while swimming
the butterfly stroke. Calculate
Duncan's speed at this instant.
34) When driven
at 2.5 m/s,
Graeme's grass
cutting machine
and Graeme
have a kinetic
energy of 3 750 J.
Calculate the combined mass of
Graeme and the machine.
35) A 1.25 kg
cannonball is
fired from a
cannon with
6 250 J of
kinetic
energy.
Calculate the speed at which the
cannonball leaves the cannon.
36) A golf ball
leaves the face
of a golf club at
40 m/s with
36.8 J of kinetic
energy.
Calculate the mass of the golf
ball.
37) Daniel and
his skis have a
combined
mass of 60 kg.
Daniel takes off
from a ski jump
with a kinetic energy of 18 750 J.
Calculate his take off speed.
Power
#
,
EW = Pt Calculations
)
Power is the amount of work done (or the amount of
energy transferred) every second.
#
,
38) A crane does 30 000 joules of
work when it lifts a load for
6 seconds. Calculate the power
of the crane engine.
41) When Lewis pulls a loaded
sledge across the snow, he
transfers 24 000 joules of energy
in 60 seconds. Calculate the
power developed by Lewis.
39) A weightlifter does
3 800 joules of work in
1.6 seconds when he lifts a set of
weights. Calculate the power
developed by the weightlifter.
42) Simon transfers 1 125 joules
of energy when he moves his
wheelchair for 15 seconds.
Calculate the power developed
by Simon.
40) An electric motor does
30 joules of work in 1.5 seconds
when it lifts a small load.
Calculate the power of the motor.
43) When a bucket is hoisted off
the ground, 390 joules of energy
is transferred in 6.5 seconds.
Calculate the power of the hoist.
)
#
&
A
Power is measured in w _ _ _ _ ( __ ).
1 w _ _ _ = 1 j _ _ _ _ per s _ _ _ _ _.
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44) Murray develops 375 watts of
power while working out for
45 seconds.
Calculate the work done.
47) An electric drill (power rating
1 250 watts) transfers
18 125 joules of energy. For what
time was the drill operated?
The Principle of Conservation of
Energy
We cannot make or destroy energy
- but we can transform (change) it
from one type to another.
A car crash is a good example of one
type of energy being converted
(changed) into other types of energy.
45) A food blender has a power
rating of 500 watts. Calculate the
work done by the blender in
15 seconds.
48) For what time does Mr. Smith
push his young son's pushchair if
Mr. Smith develops a power of
65 watts while transferring
7 800 joules of energy?
A moving car has kinetic energy. If the car
crashes into a post, the car stops moving - The
post does work on the car, bringing it to rest.
All of the car's kinetic energy is changed mainly to:
"energy of deformation" (crushing the bodywork)
heat (due to friction when the bodywork is crushed)
sound and light (sparks created when the bodywork is crushed)
50) (a) Calculate the kinetic energy of a 1 000 kg car when it
has a speed of:
46) During a tug-of-war contest,
Gillian develops 380 watts of
power as she tugs for
12.5 seconds. Calculate the
energy transferred by Gillian.
49) A chain saw develops
1 350 watts of power while doing
19 170 joules of work. Calculate
the operating time of the
chain saw.
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(b) At which of these speeds would the car do most damage if it
crashed into a wall? _____________
(c) Explain why: _____________________________________
__________________________________________________
__________________________________________________
Cars and Overall Stopping Distance
To stop a car moving, the driver applies the brakes.
The kinetic energy of the car is changed mainly to
h _ _ _ energy as a result of the force of f _ _ _ _ _ _ _
acting in the brakes and between the tyres and road.
51) (a) Why can't a car driver press the brake pedal immediately he
sees an object in the road? ________________________________
______________________________________________________
(b) This table contains information taken from the Highway Code.
The information applies to a good car with good brakes and good
tyres on a dry road with an alert driver. Complete the table:
speed of car/
miles per hour
thinking distance/ braking distance/
metres
metres
overall stopping
distance/ metres
The distance a car takes to stop depends on its
speed and hence its kinetic energy.
The shape of a speed-time graph for a "stopping" car, from the
instant the driver sees an object in the road until the car stops moving,
is shown below:
3
speed
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(c) (i) What is meant by the term "thinking distance"? __________
______________________________________________________
______________________________________________________
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(ii) No matter how fast a car is travelling, the driver always takes the
same time to react and press the brake pedal - So why does the
"thinking distance" increase as the speed of the car increases?
______________________________________________________
______________________________________________________
______________________________________________________
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(d) (i) What is meant by the term "braking distance"? ___________
______________________________________________________
______________________________________________________
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(ii) What happens to the "braking distance" as the speed of a car
increases? ___________________________________
(iii) Explain this in terms of the car's kinetic energy: _____________
______________________________________________________
______________________________________________________
Typical Energy Transformation Calculations
You will need these formulae to solve the following problems.
The problems involve the transformation (change) of energy from one type to another:
When a force moves an object through a distance,
the force does work on the object.
Work done = energy transferred.
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Power is the amount of work done (or the amount of energy
transferred) every second.
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Any object which is above ground level has
gravitational potential energy - As an object is
lifted up off the ground, work is done against
gravity. As an object is lowered down towards the
ground, work is done by gravity.
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3.6 m. Calculate the time the motor takes to do this.
Assume there is only one energy transformation (change).
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height of 4.5 m.
Calculate the time taken to do this.
Assume there is only one energy transformation
(change).
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A brick falls from the top of a 20 m high chimney. Calculate the
speed of the brick at the instant before it hits the ground.
Assume there is only one energy transformation (change).
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53) Ricky (mass 55 kg) walks up a flight of stairs for
10 s. His vertical height above the ground increases
by 5 m. Calculate the power developed by Ricky
during this activity.
Assume there is only one energy transformation
(change).
54) A 5 W electric motor takes 4.8 s to raise a 1.5 kg mass.
Calculate the height through which the mass is raised.
Assume there is only one energy transformation (change).
55) A speedboat engine applies a constant force
which causes the speedboat (mass 1 000 kg) to travel
at 25 m/s over a distance of 1 250 m.
Calculate the size of the constant force applied.
Assume there is only one energy transformation
(change).
56) A loaded sledge of mass 80 kg travels with a
speed of 3 m/s when it is pulled across the snow by
a constant force of 60 N.
Calculate the distance travelled by the sledge.
Assume there is only one energy transformation
(change).
57) A constant force of 0.12 N moves a toy car of
mass 0.02 kg at constant speed a distance of
0.75 m across a floor.
Calculate the speed of the toy car.
Assume there is only one energy transformation
(change).
58) Calculate the power developed by a jogger of
mass 62 kg who travels at 4 m/s for 124 s.
Assume there is only one energy transformation
(change).
59) A wind-up clockwork toy of mass 0.002 kg
develops a power of 0.001 W when it travels at a
constant speed for 4 s.
Calculate the value of the constant speed.
Assume there is only one energy transformation
(change).
60) An electric motor takes 12 s to pull a packing case
18 m across a smooth floor with a constant force of
200 N.
Calculate the power of the motor.
Assume there is only one energy transformation (change).
61) A cyclist develops a power of 300 W when she
applies a constant force of 250 N to the pedals of her
bike over a time of 360 s. Calculate the distance
through which the cyclist moves the pedals.
Assume there is only one energy transformation
(change).
62) Clumsy Colin drops a 1 kg brick onto his foot
from a height of 1.25 m.
Calculate the speed of the brick at the instant
before it hits his foot.
Assume there is only one energy transformation
(change).
64) A 0.5 kg cannonball is fired straight up from ground
level with a speed of 50 m/s.
Calculate the maximum height the cannonball reaches.
Assume there is only one energy transformation (change).
63) A wheel drops off a helicopter which is hovering at a
height of 45 m.
Calculate the speed of the wheel at the instant before it
strikes the ground
Assume there is only one energy transformation (change).
65) Jane the juggler throws a ball straight up in the air
with a speed of 4 m/s.
Calculate the ball's maximum increase in height above
Jane's hand.
Assume there is only one energy transformation
(change).
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