# A student pushes a heavy box along a rough floor at a constant speed. The student applies a horizontal force of 80 N and pushes the box a distance of 5 m. Explain why the work done against friction equals the work done by the student, and state what has happened to this energy at the end of the push.

> Edexcel A-Level Physics (9PH0) — 2.3 Energy and work done · Explain · 5 marks

> A student pushes a heavy box along a rough floor at a constant speed. The student applies a horizontal force of 80 N and the box moves a horizontal distance of 5 m.

## Mark scheme (5 marks)

1. Work done is calculated as force multiplied by distance (in the direction of the force) / W = F × d
2. The box moves at constant speed, so the driving force equals the friction force (forces are balanced)
3. Because the two forces are equal and act over the same distance, the work done by the student equals the work done against friction
4. The work done by the student is 400 J (80 N × 5 m)
5. The energy has been transferred to the thermal energy store of the box and the floor (due to friction) / the surroundings are heated

## Key terms

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

## 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-b2d95ac6) · Published by Druglandscape Ltd.