# A student pushes a heavy box across a rough floor at a steady speed. The student does work on the box, but the kinetic energy of the box does not increase. Explain why the kinetic energy of the box stays the same and describe what happens to the energy transferred by the student.

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

> A student pushes a heavy box across a rough floor at a steady speed. Despite the student doing work, the box does not speed up.

## Mark scheme (5 marks)

1. There is a resistive force (friction) acting on the box opposing its motion
2. The pushing force equals the resistive force / forces are balanced, so there is no resultant force
3. Because there is no resultant force, the speed does not change and so kinetic energy stays the same
4. The work done by the student is transferred to the surroundings as heat / thermal energy due to friction
5. This is dissipation of energy / the energy spreads out into the surroundings and is no longer useful

## Key terms

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

## 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-student-pushes-a-heavy-box-a0b7730b) · Published by Druglandscape Ltd.