# Homework Help: Cons. of Angular Momentum in Pool

1. Apr 16, 2009

### mikey555

1. The problem statement, all variables and given/known data

On a level billiards table a cue ball, initially at rest at point O on the table, is struck so that it leaves the cue stick with a center-of-mass speed v0 and a "reverse" spin of angular speed w0. A kinetic friction force acts on the ball as it initially skids across the table.

Explain why the ball's angular momentum is conserved about point O.

http://session.masteringphysics.com/problemAsset/1058092/3/GIANCOLI.ch11.p52.jpg

2. Relevant equations

dL/dt = 0, L = constant

3. The attempt at a solution

Here's what confuses me about this problem. When we're working with cons. of angular momentum, we assume that there are no external torques or forces. However, the stick hitting the ball is the primary torque involved. How can we say angular momentum is conserved unless we add the stick (and therefore, the person holding the stick) into the system. But I don't think this problem wants us to do that.

Thanks for the help.