# Billiard balls in headon collision with one at rest

1. Feb 8, 2004

### careysnum1fan

a billiard ball traveling 4.0m/s has an elastic head on collision witha billiard ball of equal mass that is initially at rest. the first ball is at rest after the collision. What is the the speed of the second ball after the collision?

[b(] Kim

2. Feb 8, 2004

4 m/s

3. Feb 8, 2004

### Moose352

Because the collision is elastic, kinetic energy is conserved. Since the first ball has completely stopped, its kinetic energy is 0, so the second ball takes the first's kinetic energy.

4. Feb 9, 2004

### Integral

Staff Emeritus
We must conserve momentum:

$$m_1 v_{1i}+m_{2}v_{2i}=m_1 v_{1f}+ m_2 v_{2f}$$
you are given
$$v_{1i}=4\frac m s$$
and
$$m_1=m_2$$

You should be able to complete the problem.

Last edited: Feb 9, 2004