# A rowing boat is stationary on a calm lake. A passenger steps out of the boat onto a jetty. As the passenger moves forwards, the boat moves backwards. Explain why the boat moves backwards, and why the passenger and boat eventually come to rest.

> Pearson Edexcel International GCSE Physics (4PH1) — 1.3 Forces, movement, shape and momentum · Explain · 4 marks

> A rowing boat is floating stationary on a calm lake. A passenger of mass 70 kg steps out of the boat onto a jetty. As the passenger moves forwards, the boat moves backwards.

## Mark scheme (4 marks)

1. The total momentum of the system before the passenger steps out is zero (the system is stationary).
2. By conservation of momentum, the total momentum after must also be zero, so the boat moves backwards to give equal and opposite momentum to the passenger moving forwards.
3. Newton's third law: the force the passenger exerts on the boat is equal and opposite to the force the boat exerts on the passenger, causing the boat to move in the opposite direction.
4. Friction / water resistance (on the boat) and friction (on the passenger from the jetty) act as resistive forces opposing motion, decelerating both the boat and the passenger until they stop.

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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/a-rowing-boat-is-stationary-on-e4ce5d12) · Published by Druglandscape Ltd.