1. A 75KG man stands in a 100kg rowboat at rest in still water. He faces the back of the boat and throws a 5kg rock out of the back at a speed of 20 m/s. The boat recoils forward 4.2 m.. Calculate the initial recoil spped of the boat, the loss in mecahnical energy due to friction, the effective coefficient of friction. Ok, what throws me off is that 4.2 meters that it recoils.... 2. A 0.3kg puck, at rest, is struck by a 0.2 kg puck moving along the xaxis with a speed of 2 m/'s. After the collision, the 0.2 kg puck has a speed of 1 m/s at an angle of 53 degrees to the xaxis. Find the velocity of the 0.3kg puck after the collision, find the fraction of KE lost in the collision. Momentum would be equal before and after right?