Work done and energy transfer — AQA GCSE Physics
Test yourself on Work done and energy transfer with AQA GCSE practice questions.
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Work done and energy transfer explained
Work is the name physics gives to energy transferred by a force.
Read the full explanation
A force on its own transfers nothing: a person holding a heavy box still, or pushing on a wall that will not move, does no work in the physics sense however tired they feel. The object has to move, and only the part of the movement along the line in which the force acts counts, so carrying a box horizontally at a steady height does no work against its weight. When work is done the energy comes out of one store and goes into another - chemical in a muscle or an engine into kinetic as a car speeds up, or into gravitational potential as a crate is lifted. Work done and energy transferred are the same quantity measured in joules, which is why the two phrases are interchangeable in mark schemes.
Your focus
- Decide whether work is done in a given situation by testing whether the force moves its point of application.
- Name the store energy leaves and the store it enters for a lift, a push and a braking car.
- Justify why holding a mass stationary transfers no energy by work, even though the muscle feels the effort.
Work done and energy transfer exam tips
Quick Revision Summary (Key Takeaway)
Work done is a measure of mechanical or electrical energy transfer that occurs whenever a force moves an object through a distance along the line of action. It is calculated using W = Fs, where one joule of work is done when a force of one newton displaces an object by one metre.
Topic Overview
Work done and energy transfer forms the mechanical foundation of AQA GCSE Physics Topic 1 (Energy). Whenever an object is moved by an applied force, energy is mechanically shifted out of one store and into another, meaning that 'work done' is simply another phrase for energy transferred.
Mastering this topic is essential because it bridges kinematics and dynamics with conservation of energy, power calculations, and mechanical efficiency across both Paper 1 and Paper 2. It equips students to evaluate braking systems, electric motors, and everyday forces in structured multi-step calculations.
Key Concepts
- →Work is done when a force causes an object to be displaced through a distance along the line of action of that force (W = Fs).
- →One joule of work is done when a force of one newton causes a displacement of one metre (1 J = 1 N m).
- →Work done against frictional forces acting on an object causes a rise in the temperature of the object and its surroundings, dissipating energy into thermal stores.
- →Power is the rate at which work is done or energy is transferred (P = W / t = E / t), measured in watts (W).
Marking Points
- one mark for stating that the force must move the object through a distance before any work is done
- one mark for using the distance moved along the line of action of the force, not the whole path
- one mark for naming the energy store the transfer comes from and the store it fills
- one mark for treating work done and energy transferred as the same quantity, measured in joules
Examiner Tips
- 💡Check the object actually moves before writing that work is done; a stationary object means the answer is zero.
- 💡Name the store that empties and the store that fills - examiners want the transfer named, not just the word energy.
- 💡State the base formula (e.g. W = Fs) explicitly before substituting values, as this secures method marks even if a calculation slips.
- 💡Always check whether the answer requires kilojoules (kJ) or joules (J), and round to the lowest number of significant figures provided in the question data.
- 💡When explaining friction, always use the phrase 'energy is transferred to thermal stores of the surroundings' rather than vague words like 'lost' or 'used up'.
Common Mistakes
- saying work is done while someone holds a heavy load still, when the load does not move
- using the full path length where the force acts at right angles to part of the motion, such as the weight of a bag carried along a level floor
- writing that the force makes energy rather than transferring it between stores
- confusing work done with power by leaving a time in the answer
- Thinking that holding a stationary heavy object requires work to be done on the object; because displacement is zero (s = 0), mechanical work done on the object is exactly 0 J.
- Believing that work done and energy are different physical quantities with different units; both are scalar quantities measured in joules (J).
- Assuming normal contact forces do work during horizontal motion; forces perpendicular to displacement do zero mechanical work.
Revision Plan
- 1Day 1-2: Memorise the formula W = Fs, practice standard unit conversions (cm/km to m; kJ to J), and learn the standard definition of the joule.
- 2Day 3-4: Work through combined multi-step problems that link weight (W = mg) or braking force with kinetic energy (Ek = 0.5mv^2).
- 3Day 5-6: Practice descriptive 4-6 mark questions explaining energy store transfers during friction, braking, and vertical lifting.
- 4Day 7: Complete timed past paper calculation questions from AQA Paper 1, strictly self-marking using official mark schemes.
Exam Question Types
- 📋Direct substitution calculation questions (2-3 marks): Calculate work done, force, or distance using W = Fs with unit conversions.
- 📋Multi-step energy links (4-5 marks): Combining work done against braking forces with initial kinetic energy to calculate stopping distance.
- 📋Extended response explanations (4-6 marks): Describing thermal dissipation and energy transfers when work is done against resistive forces.
Command Word Expectations (AQA)
Show clear working: state the formula, substitute converted numbers, evaluate the mathematical answer, and supply correct units.
State the key stages of an energy transfer clearly without needing to explain why; identify the start store, pathway, and destination store.
Provide a reasoning link, using cause-and-effect language (e.g. 'work done against friction causes an increase in thermal energy store').
How Students Lose Marks (Examiner Pitfalls)
Step-by-Step Worked Solutions
Question: A cyclist applies a driving force of 140 N to travel a distance of 850 m along a flat road against resistive forces. Calculate the work done by the cyclist and state the energy transfer that occurs.
- 1.Step 1: Identify given quantities and formula. Force (F) = 140 N, distance (s) = 850 m. Equation: W = F * s.
- 2.Step 2: Substitute the numerical values into the equation: W = 140 N * 850 m = 119,000 J (or 119 kJ).
- 3.Step 3: State the energy pathway. Chemical energy stored in the cyclist is transferred mechanically to kinetic energy and thermal energy stores in the surroundings via friction and air resistance.
Question: An electric hoist raises a 65 kg builder's bag of sand vertically by 4.0 m at constant speed. Gravitational field strength g = 9.8 N/kg. Calculate the work done on the sand.
- 1.Step 1: Calculate the force required to lift the sand against gravity using W_weight = m * g. Weight = 65 kg * 9.8 N/kg = 637 N.
- 2.Step 2: Use the work done formula W = F * s where s is the vertical displacement: W = 637 N * 4.0 m.
- 3.Step 3: Calculate final numerical value: W = 2548 J. Round to 2 significant figures to match the given data: 2500 J (or 2.5 kJ).