GCSE Physics equations practice
Select a relationship from the equation sheet, rearrange it and calculate with the right units.
GCSE Physics energy calculations
Calculate work, kinetic and gravitational energy, power and percentage efficiency.
Practise
Rearrange for timeA device transfers 94 kJ at a constant power of 800 W. Calculate the time taken in s. Give your answer to 3 significant figures.
Equation: P = E / t
Work through the calculation
Check intermediate steps, then use your unrounded working for the final answer. Each numerical check uses 3 significant figures. These steps provide support; the main answer is checked separately.
Step 1
Convert the energy from kJ to J. Give your answer to 3 significant figures.
Show this step
Multiply the kJ value by 1000.
Answer: 9.40 × 10^4 J (3 significant figures).
Step 2
Now calculate the final answer to the main question.
Show this step
Rearrange P = E / t to t = E / P. Convert kJ to J.
Answer: 118 s (3 significant figures).
Treat the given values as exact unless an uncertainty is stated.
Hint
Rearrange P = E / t to t = E / P. Convert kJ to J.
Worked solution
- E = 94 × 103 J.
- t = E / P = (94 × 103) / 800 s.
- Answer: 118 s (3 significant figures).
Question type: Mixed practice
Report a problem
Calculate energy and efficiency with matching units
A 2.0 kg object rises 1.5 m with g = 10 N kg⁻¹. Its gravitational energy increase is mgh = 30 J. If the lifting device receives 50 J, efficiency = 30/50 = 0.60 = 60%. The input must cover the same lifting process.
Efficiency is useful output divided by total input. A percentage needs multiplication by 100. For kinetic energy, square the speed in E = ½mv²; doubling speed gives four times the kinetic energy at unchanged mass.
Foundation and Higher: this set covers content common to both tiers. Some calculations need several steps.
Energy transfers
Work done by a force acting along the movement is force × distance. Kinetic energy uses the square of the speed; gravitational energy uses the stated gravitational field strength and height change. Useful output divided by total input gives efficiency. Multiply by 100 for a percentage. For heating and changes of state, use the separate thermal calculations resource.
GCSE scope
AQA 8463: 4.1.1.2, 4.1.1.4, 4.1.2.2; 4.5.2; OCR Gateway J249: P2.3; P7.1–2; PM2.3iv; PM2.2iii–iv; PM2.1iv, PM7.2i. Tasks cover the selected skills listed above.