Ballistic experiment
A bullet strikes a piece of wood. This piece of wood is supported by a string attached to a beam. The bullet has mass 0.015 kg and an initial speed of 600 m/s. The piece of wood has mass 1 kg.
Part of the initial (kinetic) energy of the bullet is absorbed by the wood. After the impact the piece of wood swings forward with a certain speed. The bullet continues at a lower speed or recoils with a certain speed. After the collision, the kinetic energy of the bullet and the piece of wood is a factor D tof teh initial energy before the collision.