Physics 9702 · syllabus 5
Cambridge A Level Physics 9702 — Work, energy and power topical past papers
Work as force times displacement, conservation of energy and efficiency, gravitational potential and kinetic energy, and power including P = Fv.
- Questions
- 478
- Years
- 2009–2026
- With mark scheme
- 100%
- Questions 2022–2026
- 142
Anyone can browse these pages. Opening the questions and their mark schemes takes a free Momentum account.
What Work, energy and power covers
Work is done when a force moves its point of application, and it equals the force multiplied by the displacement in the direction of the force. Doing work transfers energy, and energy is conserved: it changes form, but the total stays the same. Efficiency measures how much of the energy put into a system comes out in the form you wanted, as a ratio or a percentage.
Two energy formulae are derived here. Lifting a mass m through a height Δh in a uniform field needs a force mg acting over a distance Δh, so ΔEₚ = mgΔh. Accelerating a mass from rest with a constant force, combined with v² = u² + 2as, gives Eₖ = ½mv². You are expected to reproduce both derivations, not just quote the results.
Power is the rate of doing work. For a vehicle moving at speed v, the driving force does work at a rate P = Fv, which links this topic with dynamics: at a steady speed the driving force equals the resistive forces. Work, energy and power are AS content, examined on Papers 1 and 2, and energy arguments return in almost every A Level topic, from orbits to oscillations.
In the syllabus
The headings this topic has in the Cambridge International 2025–2027 syllabus, as the board prints them.
- 5 Work, energy and power
- 5.1 Energy conservation
- 5.2 Gravitational potential energy and kinetic energy
What you should be able to do
- Calculate work done using the component of the force along the displacement
- Derive ΔEₚ = mgΔh from W = Fs, and Eₖ = ½mv² from the equations of motion
- Apply conservation of energy to falling, sliding and launched objects, including work done against friction
- Calculate efficiency from useful output and total input, as energy or power
- Derive P = Fv and use it for vehicles moving at constant speed or accelerating
Key ideas
- Work W = Fs cos θ, where θ is the angle between the force and the displacement (J)
- ΔEₚ = mgΔh in a uniform field; Eₖ = ½mv²
- Efficiency = useful energy output ÷ total energy input (× 100%)
- Power P = W/t = Fv (1 W = 1 J s⁻¹)
How Work, energy and power has been examined
From 2022 to 2026, Work, energy and power was on Paper 2 · AS Level Structured Questions in 11 of 11 exam series, worth about 17% of that paper’s marks.
| Paper | Questions | Share of marks | Series |
|---|---|---|---|
| Paper 1 · Multiple Choice | 107 | 8% | 11 of 11 |
| Paper 2 · AS Level Structured Questions | 33 | 17% | 11 of 11 |
| Paper 4 · A Level Structured Questions | 2 | 1% | 1 of 11 |
Momentum’s own count, over the questions in its bank for these years: a series is one exam session, every zone included, and a question filed under two chapters counts in both. Median marks per question: 1.
Filed in Momentum under: Work, Energy & Power.
A worked example
A car of mass 1200 kg is driven up a road inclined at 5.0° to the horizontal at a constant 20 m s⁻¹. The resistive forces on it total 600 N. Calculate the useful output power of the engine.
- Component of weight down the slope: mg sin θ = 1200 × 9.81 × sin 5.0° = 1026 N
- At constant speed the driving force balances everything opposing the motion: F = 1026 + 600 = 1626 N
- Power: P = Fv = 1626 × 20 = 3.25 × 10⁴ W
Answer: 3.3 × 10⁴ W (about 33 kW)
Written by Momentum for this page, with its own numbers; it is not taken from a past paper.
Mistakes that cost marks
- Using the distance along a slope in mgΔh — gravitational potential energy depends on the vertical height gained, Δh = L sin θ for a slope of length L at angle θ
- Setting the driving force equal to the resistive force while the vehicle is accelerating — that balance holds only at constant speed; otherwise driving force − resistive force = ma
- Forgetting to square the speed in ½mv² — kinetic energy grows with v², so doubling the speed quadruples it
- Quoting an efficiency above 100% after dividing input by output — the useful output always goes on top
Exam technique
- In derivations, start from the definition (W = Fs, or v² = u² + 2as) and say in words what each substitution is; the final formula alone earns nothing
- For energy-conservation problems, write the energy equation in words first — loss of potential energy = gain of kinetic energy + work done against friction — then substitute
- When a power question involves a slope, resolve the weight along the slope (mg sin θ) and add it to the resistive force before multiplying by the speed
Practising in Momentum
- Every question in a chapter as one list, from every paper and year in the bank, newest first or shuffled.
- Each question turns over to its own part of the mark scheme, where the board published one.
- Narrow by paper, year, session, zone and marks, and star the questions worth keeping.
- Pick chapters, a number of questions and a time, and the exam builder draws a mock to sit and mark.
Past-paper questions and mark schemes are the copyright of Cambridge International. Momentum shows them to signed-in learners for revision and does not publish them on these pages.