10. Ballistic Pendulum

A spring gun, clamped to the lecture table, fires a steel ball into a pendulum bob, which traps it. The pendulum bob swings away and is held at the highest position reached by a ratchet. The laws of conservation of energy and momentum for the inelastic collision of the steel ball with the pendulum bob are used to calculate the velocity of the ball as fired by the gun from the data of the height of rise of the bob and the mass of the ball and the bob.

The pendulum bob is then moved out of the way so the gun can fire across the lecture hall. Tne laws of ballistics are used to calculate the spot on the floor the ball will hit, and a metal can is placed on the predicted spot to catch the ball.