Example: Ballistic Pendulum

Question:

A bullet (v = 300 m/s, m = 0.020 kg) hits a block (M = 4.0 kg) and sticks in it.

1. What is the kinetic energy of block+bullet right after impact?
2. If the block is suspended by strings, how high will this pendulum swing?

Answer:

Since this is a completely inelastic collision, we can calculate the final velocity, V, of the combination block+bullet from the formula just given:

Kinetic energy right after impact: (not conserved during collision!)

= 4.5 J

Height from conversion of kinetic energy to potential energy:

= 0.12 m