# A cyclist rides along a flat road at a constant speed. The cyclist's legs apply a force to the pedals, but the bicycle does not accelerate. Explain why the kinetic energy of the cyclist and bicycle does not increase, and describe what happens to the energy transferred by the cyclist's legs.

> WJEC A-Level Physics (Wales) — 1.3 Energy concepts · Explain · 5 marks

> A cyclist pedals continuously along a flat road at a steady speed. Despite the constant effort from the cyclist, the speed does not change.

## Mark scheme (5 marks)

1. Work is done by the cyclist's legs / a force acts over a distance, so energy is transferred into the system
2. Friction / air resistance acts against the motion of the bicycle
3. The driving force from the cyclist equals / is balanced by the resistive forces, so there is no net force
4. The energy transferred by the cyclist is a waste energy transfer — it is dissipated as thermal energy (heat) due to friction / air resistance
5. Energy is not created or destroyed — conservation of energy means the total energy input equals the total energy dissipated / the kinetic energy store stays constant because all input energy becomes waste thermal energy

## Key terms

- [kinetic energy](https://www.gradenine.co.uk/glossary/kinetic-energy)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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-04bce7bb) · Published by Druglandscape Ltd.