Work, Power & Efficiency (Edexcel GCSE Physics)

Exam Questions

3 hours15 questions
1a
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2 marks

A cyclist is riding along a straight, level road at a constant speed.

Complete the sentences with a suitable word or phrase.

As the cyclist rides along the road, energy in the .................................... energy store of the cyclist’s body decreases.

The speed of the cyclist is constant when the work done by the cyclist is .................................... the work done against air resistance.

1b
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1 mark

State the equation linking power (P), time (t) and work done (E).

1c
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3 marks

Calculate the work done by the cyclist when his power output is 460 W for 3500 seconds.

   

   

work done = .................... J

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2a2 marks

A tennis ball is dropped from a height of 2.25 m onto a smooth wooden floor, where it bounces, reaching a height of 0.86 m.

The tennis ball has a mass of 0.08 kg.

 

Use the correct scientific words to complete the sentences about the energy transfers
:
 
i)
the ball is falling towards the floor
 
 
.................................... energy store → kinetic energy store
[1]
 
ii)
the ball hits the floor and deforms
 
 
kinetic energy store → .................................... energy store
[1]
2b
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2 marks

Calculate the energy in the gravitational potential store of the ball just before it is dropped.

 
 
 energy = ....................................
2c
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4 marks

Calculate the speed at which the tennis ball hits the floor.

For the purposes of this calculation, you can assume there is no air resistance.

 
 
speed = ....................................
2d
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3 marks

The bounce height is smaller than the height the ball was dropped from. 

Explain why this is the case.

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3a
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2 marks

A group of students want to measure their power output when climbing a ladder. 

One student has a mass of 65 kg and takes 20 s to climb the ladder which has a vertical height of 2.4 m.

 

Calculate the work done in raising the student's body mass as they climb the ladder.

 
 
work = ....................................
3b
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2 marks
Calculate the student's power output in raising their body mass up the ladder.
 
 
power output = ...................................
3c
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3 marks

The student's body is only 21% efficient when climbing the ladder. 

Calculate the total power input of the student to climb the ladder. 

 
 
power input =  ....................................
3d
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2 marks

State the energy transfer taking place as the student climbs the ladder.

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1a7 marks

A cyclist has a mass of 64 kg.

i)
The cyclist rides from a flat road to the top of a hill.

The top of the hill is 24 m above the flat road.

Calculate the gain in gravitational potential energy, ∆GPE, of the cyclist.

Use g = 10 N/kg

Use the equation

   ∆GPE = m  × g × ∆h

[2]

gain in gravitational potential energy = .............................................................. J

ii)
The cyclist returns to the flat road.

The mass of the cyclist is 64 kg.

Calculate the kinetic energy of the cyclist when the cyclist is travelling at 6.0 m/s.

Use the equation

KE = 1⁄2 × m × v2

[3]

iii)
The cyclist then uses the brakes on the bicycle to stop.

Explain what happens to the kinetic energy of the cyclist.

[2]

1b3 marks

A different cyclist uses a motorised bicycle.

The motorised bicycle is powered by an electric motor.

Figure 3 is an energy diagram for the motor.

fig-3-paper1f-oct2021-edexcel-gcse-physics

Figure 3

i)
Calculate how much energy is wasted.

[1]

energy wasted = .............................................................. J

ii)
Calculate the efficiency of the electric motor.

[2]

Use the equation:

efficiency space equals space fraction numerator left parenthesis useful space energy space transferred space by space the space device right parenthesis over denominator left parenthesis total space energy space supplied space to space the space device right parenthesis end fraction

efficiency of electric motor = ..............................................................

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2a
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2 marks
Figure 7 shows a drone.

fig-7-paper2h-june2020-edexcel-gcse-physics

Figure 7

The drone has four spinning blades.

The upward force produced enables the drone to rise in the air.

The speed at which the blades spin is measured in turns per minute.

Figure 8 shows how the upward force produced by the four blades depends on the speed at which the blades spin.

fig-8-paper2h-june2020-edexcel-gcse-physics

Figure 8

Describe the relationship between upward force and speed shown by this graph.

2b
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5 marks

A different drone has a mass of 4.5 kg.

This drone rises from the ground to a height of 20 m.

i)
Calculate the change in gravitational potential energy when the drone rises through a height of 20 m.

The gravitational field strength g = 10 N/kg.

[2]

change in gravitational potential energy = .............................................................. J

ii)
State the amount of useful work done by the blades as the drone rises through 20 m.

[1]

useful work done = .............................................................. J

iii)
It takes 4 s for the drone to rise through 20 m.

Calculate the useful power developed by the blades in this time of 4 s.

[2]

useful power developed = .............................................................. W

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3a4 marks

This question is about energy changes.

Figure 11 shows a water slide.

A person travels from the top to the bottom of the water slide.

XbFelEaK_fig-11-paper2f-oct2021-edexcel-gcse-physics

Figure 11

i)
The mass of the person, m = 72 kg.
The change in vertical height, h = 7.0 m
Gravitational field strength, g = 10 N/ kg

Calculate the change in gravitational potential energy for the person.
 
Use the equation

change in gravitational potential energy = m × g × h

[2]

change in gravitational potential energy = .............................................................. J

ii)
The person comes to rest after the end of the water slide.

Explain what happens to the energy as the person comes to rest after the end of the water slide.

[2]

3b2 marks
b)
Figure 12 shows a person pushing a box from the bottom of a slope to the top of the slope.

fig-12-paper2f-oct2021-edexcel-gcse-physics

Figure 12

Explain which one of the three distances shown in Figure 12 should be used to
calculate the work done against the force of friction between the box and the slope.


(2)

3c3 marks
c)
Calculate the kinetic energy of a tennis ball travelling at 28 m/s.
The mass of the tennis ball = 58 g.

Use the equation
KE space equals space 1 half cross times straight m cross times straight v squared

(3)

kinetic energy = .............................................................. J

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4a2 marks

A cyclist is riding a bicycle at a steady velocity of 12 m/s.

The cyclist and bicycle have a total mass of 68 kg.

Calculate the kinetic energy of the cyclist and bicycle.

Use the equation

K E space equals 1 half cross times m cross times v squared

kinetic energy = ............................................... J

4b2 marks

Describe the energy transfers that happen when the cyclist uses the brakes to stop.

4c3 marks

The cyclist starts to cycle again.

The cyclist does 1600 J of useful work to travel 28 m.

Calculate the average force the cyclist exerts.


average force = ............................................... N
4d2 marks

An athlete uses a training machine in a gym.

The display on the machine shows the time spent on the machine and the amount of energy transferred during a training session.


Figure 5 shows the displays for two different sessions by the same athlete.

fig-5-paper2h-june2018-edexcel-gcse-physics

Figure 5

Explain what the displays show about the average power of the athlete in each of these two sessions.

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5a2 marks
Figure 6 shows a spinning flywheel.

fig6-paper1f-june2018-edexcel-gcse-physics
Figure 6

i)
State how energy is stored in a spinning flywheel.

[1]

ii)
State one way to increase the amount of energy stored in the flywheel.
[1]
5b5 marks
Figure 7 shows a skier going down a hill.
9Ju3U3AG_fig7-paper1f-june2018-edexcel-gcse-physics
Figure 7


She descends through a vertical height of 200 m.

The skier’s mass is 65 kg. 

i)
Calculate the change in gravitational potential energy. 

Use the equation

italic increment G P E italic equals m italic cross times g italic cross times italic increment h

Take the gravitational field strength, g, as 10 N/ kg.

[2]

change in gravitational potential energy = .................................. J

ii)
At the bottom of the slope her speed was 36 m/s.

Calculate her kinetic energy at the bottom of the slope.

Use the equation
K E equals 1 half cross times m cross times v squared
[3]

kinetic energy = .................................... J

5c3 marks

Describe how her speed at the bottom of the slope could be determined.

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6a2 marks
A student investigates how different surfaces radiate energy as they cool.

Figure 9 shows some of the apparatus used in a part of the investigation.

fig-9-ipho-1h-june18-qp-edexcel-gcse-physics

Figure 9

Describe how the student could collect data to show how the rate of cooling of the container and water change with time.

6b2 marks
Figure 10 is a graph of intensity against wavelength for the electromagnetic radiation emitted by a halogen lamp.

fig-10-ipho-1h-june18-qp-edexcel-gcse-physics
Figure 10

Describe how the intensity of the radiation varies with wavelength in Figure 10.

6c7 marks
Figure 11 is a graph of temperature against time for a halogen lamp for the first 120 ms after it has been switched on.

fig-11-ipho-1h-june18-qp-edexcel-gcse-physicsFigure 11

i)
Calculate the gradient of the graph at a time of 30 ms.
State the unit.

[4]

gradient = .............................................................. unit ................................

ii)
Explain why the temperature of the lamp rises and then remains at a constant value.

[3]

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7a5 marks

Higher Only

 

i)
Figure 14 shows the vertical forces on an aeroplane.
YKud3DHg_fig-14-paper2h-june2018-edexcel-gcse-physics

Figure 14

Use information from the diagram to determine the size and direction of the resultant vertical force on the aeroplane.

[2]

size = ................. kN, direction is ...............

ii)
The aeroplane is descending.

Figure 15 shows a diagram of the resultant vertical and horizontal forces on the aeroplane as it is descending.

fig-15-paper2h-june2018-edexcel-gcse-physicsFigure 15

Complete the diagram to show the resultant of these two forces.

[1]

iii)
The mass of the aeroplane is 750 kg.

Calculate the change in gravitational potential energy of the aeroplane as it descends from 1300 m to the ground.

Gravitational field strength (g) = 10 N/kg

[2]

energy = ........................... J

7b6 marks

The aeroplane is powered by an engine that burns fuel.

The fuel supplies a total of 6500 kJ of energy every minute.

The efficiency of the engine is 0.70 (70%).

i)
Calculate the power output of the engine.

Give your answer in kW.

[4]

power = ............................................... kW

ii)
Explain why the efficiency of the engine is less than 1 (100%).

[2]

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1a5 marks

Figure 14 shows an athlete using a fitness device.

fig-14-paper2h-june2019-edexcel-gcse-physics
Figure 14


The athlete stretches the spring in the device by pulling the handles apart.

The spring constant of the spring is 140 N/m.

The athlete does 45 J of work to extend the spring.

The athlete takes 0.6 s to expand the spring.

i)
Calculate the useful power output of the athlete when stretching the spring.
[2]
useful power output of the athlete = ............................................... W

ii)
Calculate the extension of the spring.

Use an equation selected from the list of equations at the end of this paper.

[3]

extension of the spring = ............................................... m

1b4 marks

A student investigates the stretching of a long piece of rubber.

Figure 15 shows the apparatus to be used.

fig-15-paper2h-june2019-edexcel-gcse-physics

Figure 15

The student puts just enough weight on the weight hanger to make the piece of rubber just tight.

The student wants to plot a graph to show how the extension of the piece of rubber varies with the force used to stretch it.

The student adds a known weight to the weight hanger.

i)
Describe how the student could measure the extension of the rubber when he adds another weight to the weight hanger.

[2]

ii)
The student obtains a series of values of force and extension while loading the piece of rubber and then unloading it.

Figure 16 shows the graph of the student’s values.

fig-16-paper2h-june2019-edexcel-gcse-physics

Figure 16

Explain how the shape of this graph shows that the distortion of the piece of rubber being stretched is different from the distortion of a spring being stretched.

[2]

1c2 marks

The area between the curve and the extension axis of a force/extension graph corresponds to work done or energy transferred.
Suggest what the shaded area of the graph in Figure 16 represents.

[2]

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2a
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1 mark

A resultant force of 150 N acts on a ball and moves it up a slope, as shown in Figure 1.

8-1-h-2a-work-done-slope-edx-gcse-sq

Figure 1

What is the work done on the ball as a result of the movement?

  A 45 J
  B 60 J
  C 75 J
  D 180 J
    2b
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    7 marks

    The ball has a mass of 66 g.

    i)
    Calculate the change in gravitational potential energy when the ball is lifted through a vertical height of 4.0 m.

    Use the equation
    increment G P E equals m cross times g cross times increment h

    [2]

    ii)
    The ball is released.

    Calculate the kinetic energy of the ball when the speed of the ball is 7.5 m/s.
    [3]
    iii)
    State whether the ball has reached the ground when it has a speed of 7.5 m/s. Explain why.
    [2]
    2c
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    3 marks
    i)
    The ball bounces several times.

    Figure 2 shows how the height of the ball above the floor changes with time.

    8-1-h-2c-ball-bounce-height-time-edx-gcse-sq

    Figure 2

    Use Figure 2 to estimate the maximum height that the ball reaches after the first bounce.

    [1]

    ii)
    Explain why the ball does not bounce back to its starting height of 4.0 m.
    [2]

    2d
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    2 marks

    A student plots a graph showing the height at the start and the maximum height reached after each bounce.

    Figure 3 shows the student’s graph.

    8-1-h-2d-ball-bounce-height-bounce-number-edx-gcse-sq

    Figure 3

    Describe how the maximum height reached changes with the bounce number in Figure 3.

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    3a
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    1 mark

    Two cyclists ride on a hilly road and go through points W, X, Y and Z. The diagram in Figure 1 shows how the vertical height of the road changes during the journey from W to Z.

    8-1-h-3a-height-distance-bike-ride-edx-gcse-sq

    Figure 1

    The greatest overall change in gravitational potential energy is between points

      A W and Y
      B X and Y
      C W and Z
      D X and Z

      3b
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      6 marks
      i)
      The total weight of Cyclist 1 and their bicycle is 900 N.

      Calculate the total work done against gravity when Cyclist 1 travels from point W to point X in the journey.

      [2]

      ii)
      The gravitational potential energy of Cyclist 2 changes by 12 750 J when travelling from point X to point Y.

      Calculate the mass of Cyclist 2. Take the mass of a bicycle to be 10 kg.

      Gravitational field strength = 10 N/kg

      Use the equation

      ΔGPE = m × g × Δh

      [2]

      iii)
      Explain why the total work done by a cyclist between points X and Y is different from their change in gravitational potential energy between the same points.

      [2]

      3c
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      6 marks

      The two cyclists race each other from Y to Z, both starting from rest. The efficiency of each cyclist is shown in the table in Figure 2.

      Figure 2

      cyclist efficiency final velocity at Z / m/s
      1 0.35  
      2 0.45  

       

      Determine which cyclist won the race using the information in the table in Figure 2.

      Use the equation

      K E space equals space 1 half space cross times space m italic space cross times space v squared

      3d
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      1 mark

      The next time the cyclists went on this ride, they lubricated the chains and the wheel bearings of their bicycles before setting off.

      Lubricating the chains and wheel bearings helps to

        A decrease the amount of work done against gravity
        B decrease the efficiency of the cyclist and bicycle
        C increase the efficiency of the cyclist and bicycle
        D increase the overall amount of energy transferred by the cyclist

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        4a
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        2 marks

        The work done to bring a car to rest is given by the equation

        work done = braking force × braking distance

        On the axes in Figure 1 below, sketch the variation of the car's braking distance with work done if a constant braking force is applied.

        8-1-h-4a-8-1-h-work-done-braking-distance-axes-edx-gcse-sq

        Figure 1

        4b
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        1 mark

        Before the car brakes, it has energy in its kinetic store.

        This energy decreases as it brakes.

        State what happens to the energy during braking.

        4c
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        4 marks
        The graph in Figure 2 shows how the braking distance d of a car depends on its velocity v when the brakes are first applied.



        8-1-h-4c-8-1-h-braking-distance-velocity-axes-edx-gcse-sq

        Figure 2

        The equation relating braking distance d to velocity v is

        d space equals space v squared over C

        where C is a constant.

        Use the equation and data from the graph in Figure 2 to calculate a value for C.

        Give a unit for C.

        4d
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        3 marks

        Modern electric and hybrid cars are often fitted with a regenerative braking system.

        A regenerative braking system not only slows a car down but a generator charges the car’s battery at the same time.

        Discuss one of the benefits of a regenerative braking system. Explain how this benefit is possible.

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        5a
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        3 marks

        A fairground amusement uses the arrangement shown in Figure 1 to measure the power rating of an individual.

        1-7-5b-h-power-pulley-system

        Figure 1

        In the table below, list the quantities that must be measured to determine power and an instrument that could be used for each measurement.

          quantity to be measured instrument used for measurement
        1.    
        2.    
        3.    

        5b
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        4 marks

        The mass of the load on the system is 30 kg.

        The man pulled the rope as hard as he could for a total of 5.2 s. Detectors on the pulley determined that 2.3 m of rope passed through it.

        i)
        Determine the power rating of the man.
        [3]
        ii)
        The machine on the amusement determined the man to have a power rating of 100 W.
         
        Suggest a reason for the discrepancy.
        [1]
        5c
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        2 marks

        The man inputs 2050 J of energy whilst pulling on the rope.

        Calculate the percentage efficiency of the man's body.

        5d
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        6 marks

        Another fairground amusement involves a ball on a spring.

        A student investigates how the energies of the ball and the spring change when they vibrate together.

        The diagrams and bar charts in Figure 2 show how the energies of the ball and spring vary with the position of the ball.

        The ball has a mass of 1 kg.

        8-1-h-5d-8-1-h-mass-spring-energy-changes-edx-gcse-sq

        Figure 2

        GPE = gravitational potential energy of the ball (zero at ground level)
        KE = kinetic energy of the ball
        EPE = elastic potential energy of the spring

         

        Use information from Figure 2 to describe the changes in energy, speed and position of the ball as it vibrates on the spring.

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