GCSE Physics resources

AQA GCSE Energy

Energy Calculations and Power

The changing quantity chooses the energy equation: speed, height, extension, displacement or time. A faster transfer and a larger transfer are different claims.

AQA 8463AQA 8464 GCSE PhysicsCombined Science: Trilogy FoundationHigher

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The revision snapshot

The changing quantity chooses the energy equation: speed, height, extension, displacement or time. A faster transfer and a larger transfer are different claims.

By the end, you should be able to:

  • Select an energy equation from the described change.
  • Calculate energy or power in SI units.
  • Predict how changing speed changes kinetic energy.

Before you revise

Diagnostic question

Choose an answer from memory. Your result tells you what to watch for in the guide.

A trolley of unchanged mass doubles its speed. Its kinetic energy becomes…

Read the feedback for every option
  1. Speed is squared.
  2. (2v)² = 4v².
  3. Increasing speed increases kinetic energy.
  4. Kinetic energy depends on speed.

Core revision guide

Learn the model, then use it

The changing quantity chooses the energy equation: speed, height, extension, displacement or time. A faster transfer and a larger transfer are different claims.

Match the change to its equation

Scope: 8463 and 8464 · Foundation and Higher

Use Eₖ = ½mv² for motion, Eₚ = mgh for a height change near Earth, and Eₑ = ½ke² for a spring in its proportional region. In W = Fs, s is displacement along the force. The spring’s force rises during stretching, so multiplying the final force by extension overestimates its work; its graph area is ½Fe.

Power describes a rate

Scope: 8463 and 8464 · Foundation and Higher

P = E/t = W/t. A 400 W motor transfers 400 J each second. Two motors can transfer the same 12000 J while taking different times. Greater power does not alone show greater efficiency. At fixed mass, doubling speed gives four times the kinetic energy; doubling height gives twice the gravitational change.

Handle units before using the calculator

Scope: 8463 and 8464 · Foundation and Higher

Convert grams to kilograms, centimetres to metres and minutes to seconds. Square the converted speed or extension. Keep an unrounded intermediate value, then give a sensible final precision. A joule is a newton metre of work; a watt is a joule per second.

Two motors lift identical 10 kilogram loads through 2.0 metres in different times, using 10 newtons per kilogram, so they transfer equal energy at different powers.
Both lifts transfer 200 J; the 2.0 s lift has twice the power of the 4.0 s lift.Open the full-size exam diagram
Kinetic energyEₖ = ½mv²J, kg, m/s
Gravitational potential energyEₚ = mghJ, kg, N/kg, m
Elastic potential energyEₑ = ½ke²J, N/m, m
PowerP = E ÷ tW, J, s

Misconception clinic

Replace the tempting answer

Read each belief, say what is wrong with it, then compare your correction.

Tempting idea: Twice as large.

Use instead: Speed is squared. (2v)² = 4v².

Tempting idea: 300000 s.

Use instead: This multiplies instead of dividing. t = E/P = 6000/50.

Retrieval practice

Quick checks

1. A 50 W motor transfers 6000 J. How long does it run?

Read the feedback for every option
  1. t = E/P = 6000/50.
  2. This multiplies instead of dividing.
  3. This calculates P/E.
  4. The joule/watt ratio gives seconds.

Worked examples

See the method being built

Apply match the change to its equation in the worked reasoning, then try the changed-context questions below.

Example 1 · Gravitational potential energy

Scope: 8463 and 8464 · Foundation and Higher

A 2.0 kg box is raised 4.0 m. Take g = 9.8 N/kg. Calculate the energy gained.

  1. Choose E = mgh.
  2. Substitute 2.0 × 9.8 × 4.0.
  3. Give joules.
Show the answer

E = 78.4 J, so the box gains 78 J to two significant figures.

Example 2 · Kinetic energy

Scope: 8463 and 8464 · Foundation and Higher

A 0.80 kg football moves at 5.0 m/s. Calculate its kinetic energy.

  1. Use Eₖ = ½mv².
  2. Square the speed before multiplying.
  3. Keep mass in kg.
Show the answer

Eₖ = 0.5 × 0.80 × 5.0² = 10 J.

Example 3 · Power

Scope: 8463 and 8464 · Foundation and Higher

A hoist transfers 12 000 J in 30 s. Calculate its power.

  1. Use P = E ÷ t.
  2. Substitute 12 000 ÷ 30.
  3. Give watts.
Show the answer

P = 400 W.

Exam precision

Use the physics precisely

Do this: Identify the change, choose its equation, convert units and substitute. Keep energy in joules distinct from power in watts.

Independent practice

Exam-style questions

Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.

1. A 0.60 kg trolley travels at 5.0 m/s. Calculate its kinetic energy.

[3 marks]

Scope: 8463 and 8464 · Foundation and Higher

Show marking guidance and model answer

Original PhysicsUK mark scheme: Point 1 (1 mark): Eₖ = ½mv². Point 2 (1 mark): Eₖ = 0.5 × 0.60 × 5.0². Point 3 (1 mark): Eₖ = 7.5 J. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.

  1. Eₖ = ½mv². (1 mark)
  2. Eₖ = 0.5 × 0.60 × 5.0². (1 mark)
  3. Eₖ = 7.5 J. (1 mark)

Model answer: Eₖ = ½mv². Eₖ = 0.5 × 0.60 × 5.0². Eₖ = 7.5 J.

Acceptable answers: Expected result: Eₖ = 7.5 J. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.

Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.

2. A 120 W hoist transfers 18000 J. Calculate the operating time.

[3 marks]

Scope: 8463 and 8464 · Foundation and Higher

Show marking guidance and model answer

Original PhysicsUK mark scheme: Point 1 (1 mark): t = E/P. Point 2 (1 mark): t = 18000/120. Point 3 (1 mark): t = 150 s. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.

  1. t = E/P. (1 mark)
  2. t = 18000/120. (1 mark)
  3. t = 150 s. (1 mark)

Model answer: t = E/P. t = 18000/120. t = 150 s.

Acceptable answers: Expected result: t = 150 s. Accept the unrounded value or a correctly rounded equivalent to two or more significant figures; accept equivalent units if converted correctly. No additional measurement interval is implied.

Marking notes: Method marks remain available after an arithmetic error. Carry an earlier numerical error into a later valid step; award that method point if the unit conversion and physics are correct. A fully correct answer with unit earns all marks unless working is expressly requested.

Questions pupils ask

Energy Calculations and Power FAQs

Does doubling speed double the energy a vehicle must lose?

No. At fixed mass its kinetic energy increases fourfold because speed is squared.

Useful next steps

Connect this guide to your next task

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