Download Measuring Energy

Standard Grade Physics
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"Measuring Energy"
Name: ________________________
Class: _____
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.
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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.
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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
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Power is the amount of work done (or the amount of
energy transferred) every second.
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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.
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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:
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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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Kinetic energy is movement energy - It depends
on the mass and speed of the moving object.
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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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A 10 W electric motor lifts a 0.5 kg mass through a height of
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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