GCSE Physics resources
AQA GCSE Energy
Choose an equation from the physical change, convert every quantity to SI units and show the substitution.
Start here
Match the equation to the physical change: speed for kinetic energy, height for gravitational potential energy, extension for elastic energy, force and distance for work done, and time for power. Convert units before substitution.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Energy Calculations and Power questions become manageable when the central model, evidence and exam method are kept together. Read the explanation, test the misconception and then apply the idea without looking back.
Match the equation to the physical change: speed for kinetic energy, height for gravitational potential energy, extension for elastic energy, force and distance for work done, and time for power. Convert units before substitution.
The words in the question choose the model. Height points to gravitational potential energy, speed to kinetic energy, extension to elastic potential energy and time to power. Write quantities in SI units before putting numbers into an equation.
Kinetic energy: Eₖ = ½mv² (J, kg, m/s). Gravitational potential energy: Eₚ = mgh (J, kg, N/kg, m). Elastic potential energy: Eₑ = ½ke² (J, N/m, m). Power: P = E ÷ t (W, J, s). Choose each relationship from the physical change described, convert quantities into compatible units and keep the unit beside the final answer.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: Using minutes with watts without converting to seconds.
Use instead: Match the equation to the physical change: speed for kinetic energy, height for gravitational potential energy, extension for elastic energy, force and distance for work done, and time for power. Convert units before substitution.
Tempting idea: Forgetting to square speed or extension.
Use instead: The words in the question choose the model. Height points to gravitational potential energy, speed to kinetic energy, extension to elastic potential energy and time to power. Write quantities in SI units before putting numbers into an equation.
Tempting idea: Choosing an equation without linking it to the changing quantity.
Use instead: Underline the changing quantity, write the equation, substitute with SI units, calculate and check whether the scale and unit make sense.
Retrieval practice
Worked examples
These examples expose the difference between a secure choosing the right energy equation method and the common error “Using minutes with watts without converting to seconds.”.
E = 78.4 J, so the box gains 78 J to two significant figures.
Eₖ = 0.5 × 0.80 × 5.0² = 10 J.
P = 400 W.
Exam precision
Do this: Underline the changing quantity, write the equation, substitute with SI units, calculate and check whether the scale and unit make sense.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Marking guidance: Award one mark for the correct relationship, one for a valid substitution and one for the final answer with its unit.
Model answer: Eₖ = ½mv² = 0.5 × 1.5 × 4.0² = 12 J.
Marking guidance: Award one mark for the correct relationship, one for a valid substitution and one for the final answer with its unit.
Model answer: E = mgh = 0.20 × 10 × 3.0 = 6.0 J.
Marking guidance: Award one mark for the correct relationship, one for a valid substitution and one for the final answer with its unit.
Model answer: Eₑ = ½ke² = 0.5 × 200 × 0.10² = 1.0 J.
Marking guidance: Award one mark for the correct relationship, one for a valid substitution and one for the final answer with its unit.
Model answer: Convert 5.0 min to 300 s. E = Pt = 60 × 300 = 18 000 J.
Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.
Model answer: It transfers energy to the water at a greater rate.
Marking guidance: Award one mark for the precise statement shown in the model answer.
Model answer: Check mass is in kg and height is in m; g should be in N/kg.
Questions pupils ask
Match the equation to the physical change: speed for kinetic energy, height for gravitational potential energy, extension for elastic energy, force and distance for work done, and time for power. Convert units before substitution.
Using minutes with watts without converting to seconds. The words in the question choose the model. Height points to gravitational potential energy, speed to kinetic energy, extension to elastic potential energy and time to power. Write quantities in SI units before putting numbers into an equation.
Useful next steps