An 80.0 kg man playing hockey catches a puck moving at 20.0 m/s. The man is initially at rest. The man and puck move together after the collision. The puck's mass is 0.17 kg. What is the final velocity?

Using conservation of momentum, the initial momentum of the man is 0, and the puck's is 0.17kg*20m/s=3.4 kg*m/s. The final mass is 80.17kg. The final momentum is still p=mv=3.4kg*m/s, so v=3.4/80.17 = 0.0424m/s