# A cyclist rides along a flat road at a constant speed. The cyclist does work against air resistance and friction. Explain why the cyclist must continuously do work to maintain a constant speed, and describe what happens to the energy that is transferred to the surroundings.

> Edexcel A-Level Physics (9PH0) — 8.2 Standard model and conservation laws · Explain · 5 marks

> A cyclist travels at a steady speed along a flat road. The cyclist's muscles provide a driving force, but resistive forces act against the motion.

## Mark scheme (5 marks)

1. A resistive force (air resistance / friction) opposes the motion of the cyclist
2. Work is done against the resistive force, so energy is transferred from the cyclist to the surroundings
3. At constant speed, the driving force equals the resistive force (forces are balanced)
4. The energy transferred to the surroundings is dissipated as heat (thermal energy)
5. The total energy is conserved — energy is not created or destroyed, only transferred; the system is less useful because the dissipated energy is spread out and cannot be recovered to do useful work

## Key terms

- [constant speed](https://www.gradenine.co.uk/glossary/constant-speed)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-cyclist-rides-along-a-flat-3dd080b5) · Published by Druglandscape Ltd.