Download Velocity is - Noadswood Science

Additional Physics – Forces
Exam Date -
“The need
for speed”
L/O :- To be able to calculate acceleration
Quick quiz
• What can the motion be like of an object with
BALANCED forces? (2 marks)
• What can the motion be like of an object with
UNBALANCED forces (2 marks)
• How do you work out speed?
• What does this distance time graph tell you about the
journey?
These cars all have the same speed
but different velocities. Why is this?
So what is the difference
between speed and velocity?
How can you work out velocity?
Speed vs. Velocity
Speed is simply how fast you are travelling…
This car is travelling at a
speed of 20m/s
Velocity is “speed in a given direction”…
This car is travelling at a
velocity of 20m/s east
22/05/2017
These vehicles all have a similar engine size (roughly 300
horse power) Which one will accelerate the fastest and why?
11339kg
The bike will have the fastest acceleration
because it has the lowest mass
You can prove this using the equation
F = m x a
F
mxa
Use the equation
to check your
predictions
1273kg
281kg
Acceleration
V-U
Acceleration = change in velocity (in m/s)
(in m/s2)
time taken (in s)
Don’t forget to underline the key info in an exam
A
T
1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What
is her acceleration?
2) A ball is dropped and accelerates downwards at a rate of
10m/s2 for 12 seconds. How much will the ball’s velocity
increase by?
3) A car accelerates from 10 to 20m/s with an acceleration of
2m/s2. How long did this take?
4) A rocket accelerates from 1,000m/s to 5,000m/s in 2
seconds. What is its acceleration?
Velocity-time graphs
1) Upwards line =
80
Velocity
m/s
4) Downward line =
60
40
20
0
10
2) Horizontal line =
22/05/2017
20
30
40
50
3) Upwards line =
T/s
80
60
Velocity
m/s
40
20
0
T/s
10
20
30
40
1) How fast was the object going after 10 seconds?
2) What is the acceleration from 20 to 30 seconds?
3) What was the deceleration from 30 to 50s?
4) How far did the object travel altogether?
50
The time starts when the boy gets on the bike. All times
must be recorded as how many seconds after this.
Incident
Boy gets
on bike
[A]
Leaps
bike over
hedge [B]
Bike
swerves
in front
of lorry
[C]
Speed
(m/s)
0
6
6
Time (s)
Lorry hits Bike goes
first car
down
[D]
ramp [E]
9
9
Bike
stops
near
bridge [F]
0
The time starts when the boy gets on the bike. All times must be recorded as how many seconds after this.
Incident
Speed (m/s)
Time (s)
Boy gets on
bike [A]
Leaps bike over
hedge [B]
Bike swerves in
front of lorry
[C]
Lorry hits first
car [D]
Bike goes down
ramp [E]
Bike stops near
bridge [F]
0
6
6
9
9
0
Incident
We first see
Terminator [G]
Terminator shoots
at gate chains
Terminator’s bike
drops into drain
Lorry’s tyre is
burst [H]
Lorry explodes [I]
Speed (m/s)
12
12
12
12
0
Time (s)
Incident
Boy gets
on bike
[A]
Speed
(m/s)
0
Bike
Leaps
Lorry hits Bike goes Bike stops
swerves in
bike over
first car
down
near
front of
hedge [B]
[D]
ramp [E] bridge [F]
lorry [C]
6
6
9
9
0
Time (s)
Incident
We first
see
Terminator
[G]
Speed
(m/s)
12
Time (s)
Terminator Terminator’s
Lorry’s tyre
Lorry
shoots at
bike drops
is burst [H] explodes [I]
gate chains
into drain
12
12
12
0
Task 2
1.
Plot the results above on a speed-time graph, with the x-axis labelled
time and the y-axis labelled speed.
2.
At each point where the boys changes motion should be labelled with the
letter A, B, C, … The point (0,0) should be labelled A.
3.
Use the shape of your graph to label the point where you expect
acceleration to be
a) fastest
b) slowest
4.
Work out the following accelerations:
A to B
B to C
C to D
D to E
E to F
F to G
G to H
H to I
1.
The manufacturer of a family car gave the following information.
Mass of car
950 kg.
The car will accelerate from 0 to 33 m/s in 11 seconds.
(a)
Calculate the acceleration of the car during the 11 seconds
.....................................................................................................................................
.....................................................................................................................................
Answer .............................................................
(2)
(b)
Calculate the force needed to produce this acceleration.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)
(c)
The manufacturer of the car claims a top speed of 110 miles per hour. Explain
why there must be a top speed for any car.
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
2.
The graph shows the speed of a runner during an indoor 60 metres race.
B
10
speed
(metres per
second)
A
C
5
0
0
2
4
6
time (seconds)
8
10
(a) Choose words from this list to complete the sentences below.
moving at a steady speed
slowing down
speeding up
stopped
Part A of the graph shows that the runner is .............................................................
Part B of the graph shows that the runner is .............................................................
Part C of the graph shows that the runner is .............................................................
(3) (b)
Calculate the acceleration of the runner during the first four seconds. (Show your
working.)
.................................................................................................................................... (3)
3.
(a) The diagram below shows a moving tractor. The forward force from the
engine exactly balances the resisting forces on the tractor.
(i) Describe the motion of the tractor.
.........................................................................................................................
(ii) The tractor comes to a drier part of the field where the resisting forces are less. If the
forward force from the engine is unchanged how, if at all, will the motion of the tractor be
affected?
.........................................................................................................................
......................................................................................................................... (3)
(b) Two pupils are given the task of finding out how fast a tractor moves across a field. As the tractor starts a straight
run across the field the pupils time how long it takes to pass a series of posts which are forty metres apart. The results
obtained are shown in the table below.
(i)
Draw a graph of distance travelled against time taken using the axes on the graph below. Label your graph line A.
200
Distance travelled (m)
0
40
80
120
160
200
Time taken (s)
0
8
16
24
32
40
180
(2)(ii) Calculate the speed of the tractor.
.....................................................................
160
In another, wetter field there is more resistance to the
movement of the tractor. It now travels at 4 m/s.
(i) Calculate the time needed to travel 200m.
............................................................................
140
120
Distance
100
(m)
(ii) On the graph in part (b) draw a line to represent the
motion of the tractor across the 2nd field. Label this line B.
(4) (d) On a road the tractor accelerates from rest up to a
speed of 6 m/s in 15 seconds.
Calculate the acceleration of the tractor.
..................................................................................................
..................................................................................................
..................................................................................................
...............................................Acceleration = ..................m/s²
(3) (Total 15 marks)
80
60
40
20
0
0
10
20
Time (s)
30
40
4.
The graph shows the speed of a runner during an indoor 60 metres race.
10
Speed
(metres per
second)
5
0
0
2
4
6
Time (seconds)
8
10
(a) Calculate the acceleration of the runner during the first four seconds. (Show your working.)
..........................................................................................................................................................................
..........................................................................................................................................................................
(b) How far does the runner travel during the first four seconds? (Show your working.)
..........................................................................................................................................................................
..........................................................................................................................................................................
(c) At the finish, a thick wall of rubber foam slows the runner down at a rate of 25 m/s2. The runner
has a mass of 75kg. Calculate the average force of the rubber foam on the runner. (Show your working.)
..........................................................................................................................................................................
..........................................................................................................................................................................
Answer ......................... newtons (N)
(2)
5.
The manufacturer of a family car gave the following information.
Mass of car 950 kg
The car will accelerate from 0 to 33 m/s in 11 seconds.
(a)
Calculate the acceleration of the car during the 11 seconds.
.....................................................................................................................................
.....................................................................................................................................
..................................................................................................................................... (2)
(b)
Calculate the force needed to produce this acceleration.
.....................................................................................................................................
.....................................................................................................................................
..................................................................................................................................... (2)
(c)
The manufacturer of the car claims a top speed of 110 miles per hour. Explain
why there must be a top speed for any car.
.....................................................................................................................................
.....................................................................................................................................
..................................................................................................................................... (3)
(Total 7 marks)
6.
A rollercoaster car stops above a vertical drop. Suddenly it falls under gravity.
The drop is 60 metres high and at the bottom of the drop the
car travels at 125 km/h.
The acceleration experienced by the people in the car is 10 m/s2.
The mass of the car and its
passengers is 1210 kg.
Calculate the force exerted on the car and its passengers.
Show your working.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
Force = ........................... N
(Total 3 marks)
What have you learnt?
• Do you know what the difference between speed and
velocity is?
• Do you know how to work out acceleration?
• Do you know which way the axes on a velocity-time
graph go?
• Do you know how to work out acceleration from a
velocity-time graph?