A 60.0 kg girl stands up on a stationary floating raft and decides to go into shore. She dives off the 180 kg floating raft with a velocity of 4.0 m/s [W]. Ignore the substantial friction real objects in water experience.

Question

What is the speed of the raft just after the girl dives?

Answer 1

conserve momentum. With everything initially at rest, momentum is zero.

So, the raft moves in the opposite direction when she jumps.

So, the speed s of the raft is such that

180s = 60*4

I note that you asked for speed, so I ignored the direction of the velocity. I expect you can figure that out.