A delivery driver pushes a heavy box along a warehouse floor at a constant speed. Explain why energy is dissipated during this process and describe the effect this has on the efficiency of the transfer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A delivery driver applies a horizontal force to push a heavy box along a rough warehouse floor. The box moves at a constant speed across the floor.
Model answer (4 marks)
1. Friction between the box and the rough floor is a resistive force that opposes the driver’s push.
2. The driver’s force does work against this friction, so mechanical energy is converted into heat.
3. The heat energy spreads into the surroundings and cannot be recovered as useful work – it is dissipated.
4. Because part of the driver’s input energy is lost as dissipated heat, the useful output energy is less than the total input, so the transfer efficiency is less than 1 (or 100%).
2. The driver’s force does work against this friction, so mechanical energy is converted into heat.
3. The heat energy spreads into the surroundings and cannot be recovered as useful work – it is dissipated.
4. Because part of the driver’s input energy is lost as dissipated heat, the useful output energy is less than the total input, so the transfer efficiency is less than 1 (or 100%).
Examiner tips
- Use the word ‘friction’ and ‘resistive force’ to show understanding of the force involved.
- Explain that work against friction produces heat and that this heat is lost to the surroundings.
- State that the loss of energy reduces the useful output, giving a numerical efficiency <1.
- Keep the answer concise and match the four mark points exactly.
Common mistakes
- Confusing friction with a non‑resistive force or ignoring it altogether.
- Claiming that all energy is converted to useful work and ignoring heat loss.
- Using vague terms like ‘energy loss’ without specifying heat or dissipation.
Mark scheme (4 marks)
- Friction is a resistive force acting against the motion of the box
- Work is done against the resistive force, causing energy to be transferred as heat to the surroundings
- This transferred heat energy is dissipated — it is spread out into the surroundings and cannot be recovered as useful energy
- Because some input energy is wasted as dissipated heat, the useful output energy is less than the total input energy, so efficiency is less than 1 (or 100%)
Key terms in this question
Related
- All Edexcel GCSE Physics (1PH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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