I'd appreciate a hint on how to start this one. "A person weighing 50kg is riding in a 400kg boat heading due east at 3.0 m/s. The person jumps horizontally out of the boat in the other direction (i.e., westward). Just after he jumps, the velocity of the boat as seen from the person is 4.5 m/s. Determine the velocity of the boat relative to the water surface just after he jumps." I assume the water is motionless. This seems like another conservation of momentum problem. The initial momentum of the boat with the person riding it is 1,350 kgms. Would this equal the difference between the man's momentum after jumping and the boat's momentum after he jumped?