# Explain why the work done by the normal contact force on a car travelling along a horizontal road is zero, even though the car moves a considerable distance.

> IB DP Physics Standard Level (2023 syllabus) — A.3 Work, energy and power · Explain · 4 marks

> A car travels at constant speed along a straight, horizontal road. The car's weight acts vertically downward and a normal contact force acts vertically upward from the road surface.

## Mark scheme (4 marks)

1. Work is defined as the product of force and the displacement in the direction of the force (or the component of force in the direction of displacement).
2. The normal contact force acts vertically upward (perpendicular to the road surface).
3. The displacement of the car is horizontal, so the angle between the normal contact force and the displacement is 90°.
4. Because cos 90° = 0, the work done by the normal contact force is zero regardless of the magnitude of the force or the distance travelled.

## Key terms

- [work](https://www.gradenine.co.uk/glossary/work)
- [normal contact force](https://www.gradenine.co.uk/glossary/normal-contact-force)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](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/explain-why-the-work-done-by-4aa3a4eb) · Published by Druglandscape Ltd.