Physics · Unit 13

Work, Energy and Power

Energy that gets things done

Work has a strict meaning here: force times distance moved in the direction of the force. Holding something heavy without moving it is exhausting and, in this sense, no work at all.

The unit covers work done, kinetic and potential energy, conservation, power as the rate of doing work, and efficiency.

This unit breaks down into 20 short steps and 118 questions, starting at difficulty 2 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 118
Difficulty: 2-3

What this unit covers

Work Done
Kinetic and Potential Energy
Power
Conservation of Energy
Efficiency and Machines

Where this fits

Needs Forces and Newton's Laws and Energy and Its Forms.

Where people slip

Power and energy are different quantities. A powerful engine delivers energy faster; it does not contain more.

How the unit is structured

Work, Energy and Power runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 2 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 118 in the unit altogether.

Conservation of Energy

Build the sentenceLevel 2
1. Build the key idea behind conservation of energy.
Answer: Energy is never created or destroyed
Energy is never created or destroyed, only transferred or changed in form.
Fact or fibLevel 2
2. Friction between moving parts usually wastes some energy as heat.
Answer: True
Friction transfers useful energy into heat, which is why moving parts warm up.
Fill the blankLevel 2
3. The law of ____ of energy says that energy cannot be created or destroyed.
- conservationcorrect
- gravity
- motion
- friction
This is the principle of conservation of energy.
Guess the numberLevel 2
4. A 2 kg ball is dropped from a height of 5 m. Ignoring air resistance, how much kinetic energy does it have just before landing? (take g = 10 N/kg)
Answer: 100 J
All the potential energy converts to kinetic energy, so KE = mass x g x height = 2 x 10 x 5 = 100 J.
Match the pairsLevel 2
5. Match each device to the main energy change it carries out.
Answer: Battery = Chemical to electrical; Torch bulb = Electrical to light; Electric motor = Electrical to kinetic; Loudspeaker = Electrical to sound
Each device transfers energy from one useful form into another.
Choose all that applyLevel 3
6. In a real roller coaster where friction is present, which statements are correct?
- Mechanical energy decreases over timecorrect
- Some energy is converted into thermal energycorrect
- Total energy including heat is conservedcorrect
- Friction destroys energy completely
Friction steadily reduces mechanical energy and produces heat, but the total energy including heat is still conserved; energy is never destroyed.

Efficiency and Machines

Fill the blankLevel 2
7. In most machines, wasted energy is usually given off as ____.
- heatcorrect
- food
- water
- gravity
Friction and moving parts turn wasted energy mainly into heat.
Guess the numberLevel 2
8. A machine takes in 100 J and delivers 80 J of useful energy. What is its efficiency as a percentage?
Answer: 80 %
Efficiency = useful energy out / total energy in x 100 = 80 / 100 x 100 = 80 percent.
Multiple choiceLevel 2
9. How do you calculate the efficiency of a machine?
- Useful energy out divided by total energy incorrect
- Total energy in divided by useful energy out
- Useful energy out multiplied by total energy in
- Total energy in minus useful energy out
Efficiency is the useful energy transferred out divided by the total energy put in.
Odd one outLevel 2
10. Which of these is NOT a simple machine?
- Batterycorrect
- Lever
- Pulley
- Inclined plane
A lever, pulley and inclined plane are simple machines, but a battery is an energy source, not a machine.
Sort into groupsLevel 2
11. Sort each energy output from these machines as useful or wasted.
Answer: Light from a lamp = Useful energy; Heat from a lamp = Wasted energy; Motion from a fan = Useful energy; Sound from a fan = Wasted energy
The energy that does the intended job is useful; the rest, often heat and sound, is wasted.
Choose all that applyLevel 3
12. Which of these are common ways a real petrol engine wastes energy? Select all that apply.
- Friction between moving partscorrect
- Heat carried away in the hot exhaust gasescorrect
- Sound and vibrationcorrect
- Increasing the chemical energy of the fuel
Friction, hot exhaust gases and sound all carry away energy; the fuel's chemical energy is the input, not a loss.

Kinetic and Potential Energy

Choose all that applyLevel 2
13. Which changes would increase a moving object's kinetic energy? Select all that apply.
- Increasing its speedcorrect
- Increasing its masscorrect
- Painting it red
- Moving it in the dark
Kinetic energy grows with both greater speed and greater mass.
Fact or fibLevel 2
14. A heavy book resting on a high shelf has gravitational potential energy.
Answer: True
Its height above the ground gives it stored gravitational potential energy.
Fill the blankLevel 2
15. Energy stored in an object because of its height above the ground is called ____ energy.
- potentialcorrect
- kinetic
- sound
- electrical
Height above the ground gives gravitational potential energy.
Guess the numberLevel 2
16. A 2 kg ball moves at 3 m/s. What is its kinetic energy? (KE = one half x mass x speed squared)
Answer: 9 J
KE = 0.5 x 2 x 3 x 3 = 9 J.
Build the sentenceLevel 3
17. Arrange the words to state the kinetic energy formula in words.
Answer: half the mass times speed squared
Kinetic energy equals half the mass times the speed squared, matching KE = half m v^2.
Match the pairsLevel 3
18. Match each energy quantity to the formula used to calculate it.
Answer: Kinetic energy = one half m v squared; Gravitational potential energy = m g h; Elastic potential energy = one half k x squared; Work by a constant force = F d cos theta
Each mechanical energy term has its own standard expression relating it to mass, speed, height or extension.

Power

Guess the numberLevel 2
19. A machine does 200 J of work in 4 s. What is its power? (Power = work / time)
Answer: 50 W
Power = 200 J divided by 4 s = 50 W.
Multiple choiceLevel 2
20. What is the SI unit of power?
- The wattcorrect
- The joule
- The newton
- The metre
Power is measured in watts, where one watt is one joule per second.
Tap the pairsLevel 2
21. Tap each quantity together with its matching unit.
Answer: Power = watt; Energy = joule; Force = newton; Speed = metre per second
Power is in watts, energy in joules, force in newtons and speed in metres per second.
True or falseLevel 2
22. A more powerful machine can do the same amount of work in less time.
Answer: True
Higher power means energy is transferred faster, so the same work is done more quickly.
Build the sentenceLevel 3
23. Build the equation for the power delivered by a force moving an object at constant velocity.
Answer: power equals force times velocity
For steady motion, power equals force times velocity, which comes from dividing work (force times distance) by time.
Fill the blankLevel 3
24. One watt is equal to one ____ per second.
- joulecorrect
- newton
- coulomb
- metre
Power is the rate of energy transfer, so one watt equals one joule per second.

Work Done

Build the sentenceLevel 2
25. Build the correct definition of work done.
Answer: Work equals force times distance
Work equals force times distance moved in the direction of the force.
Fill the blankLevel 2
26. Work is done only when a force moves an object in the ____ of the force.
- directioncorrect
- colour
- temperature
- price
Work depends on movement along the direction of the applied force.
Guess the numberLevel 2
27. A force of 50 N pushes a box 4 m in the direction of the force. How much work is done?
Answer: 200 J
Work equals force times distance, so 50 N times 4 m gives 200 J.
Match the pairsLevel 2
28. Match each physical quantity to its correct SI unit.
Answer: Work = joule; Force = newton; Distance = metre; Time = second
Work is in joules, force in newtons, distance in metres and time in seconds.
Multiple choiceLevel 2
29. Which formula gives the work done by a force?
- Work = force x distancecorrect
- Work = mass x speed
- Work = force / distance
- Work = distance / time
Work done equals the force multiplied by the distance moved in the direction of the force.
Choose all that applyLevel 3
30. Which statements about work are correct?
- Work is a scalar quantitycorrect
- Work can be negativecorrect
- The unit of work is the joulecorrect
- Work is a vector with its own direction
Work is a scalar measured in joules and can be negative when a force opposes motion; it has no direction of its own.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 16 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Work, Energy and Power

118 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Work, Energy and Power

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

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