Physics 120/130

Calculation of Trajectories using Conservation Laws

I. Introduction

The laws of conservation of momentum and energy are two of the fundamental laws of physics. We will investigate these laws by using a device called a ballistic pendulum. In the process, we will also be able to review the laws of kinematics as they apply to projectile motion. 

The ballistic pendulum is an apparatus in which a ball is shot by a gun into a suspended holder which is arranged to swing as a pendulum. When the ball is shot into the holder, it will swing to some maximum height. By measuring the height to which the holder and ball (the "system") rises and by using the conservation of energy, the velocity of the system after impact is obtained. By equating the momentum of the system immediately after impact to the momentum of the ball before its impact with the holder, the initial velocity of the ball is determined.  

We wish to measure the initial velocity of the ball in this way so that we can use the kinematic equations to predict how far the ball will be shot in projectile motion.