Physics
posted by physics .
A boxer punches a 50 Kg bag. Just as his fist hits the bag, it travels at a speed of 7 m/s. As a result of hitting the bag, his hand comes to a complete stop. Assuming that the moving part of his hand weigh 5 Kg, calculate the rebound velocity and kinetic energy of the bag.

Momentum is conserved. initial momentum of the fist, that has to equal the final momentum of the bag. Calculate its velocity, then its KE.