# Explain why the work done by the gravitational force on a satellite moving in a circular orbit around the Earth is zero, and state what this implies about the satellite's kinetic energy.

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

## Mark scheme (4 marks)

1. The gravitational force acts along the radius (centripetally), directed towards the centre of the Earth.
2. For a circular orbit, the velocity (displacement) of the satellite is always tangential, i.e. perpendicular to the gravitational force.
3. Work done W = Fs cosθ, and since θ = 90°, cos 90° = 0, so W = 0.
4. Since no work is done on the satellite, by the work–energy theorem its kinetic energy (and therefore its speed) remains constant.

## Key terms

- [work done](https://www.gradenine.co.uk/glossary/work-done)
- [gravitational force](https://www.gradenine.co.uk/glossary/gravitational-force)
- [circular orbit](https://www.gradenine.co.uk/glossary/circular-orbit)
- [kinetic energy](https://www.gradenine.co.uk/glossary/kinetic-energy)

## Related

- [Revision notes for IB DP Physics Higher 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-work-done-by-d7623924) · Published by Druglandscape Ltd.