What is the speed of the raft?

Question

A swimmer witha mass of 75kg dives off a raft with a mass of 500kg. If the swimmer's speed is 4m/s immediatley after leaving the raft, what is the speed of the the raft?

Answer 1

Conservation of momentum. This is the same as your other problem. Replace astronaut and wrench in this solution with raft and diver.

Initial momentum = 0
=
Final momentum
= mwrench vwrench + mastro vastro

So vastro = - vwrench * (mwrench / mastro)

The minus reflects the fact that he recoils the other way. Ignore it if you just want speed.

Answer 2

both forces should balance

so 75 * 4 = 500 * x
or x = (75 * 4 )/ 500
x = 0.6 m/s

Answer 3

75/500*4m/s = 0.6m/s