# Homework Help: Uniform Circular Motion: Speed of the bullet

1. Sep 12, 2009

### mehacute

1. The problem statement, all variables and given/known data
Derive a formula for the bullet speed v in terms of D, T, and a measured angle theta between the position of the hole in the first disk and that of the hole in the second. If required, use pi, not its numeric equivalent. Both of the holes lie at the same radial distance from the shaft. theta measures the angular displacement between the two holes; for instance, \theta = 0 means that the holes are in a line and \theta=\pi means that when one hole is up, the other is down. Assume that the bullet must travel through the set of disks within a single revolution.

2. Relevant equations

So, I know that speed = 2*pi*r/t and that speed = r*omega. but I don't know how to factor in the theta. Can someone please derive the whole thing and explain? Thank you.

3. The attempt at a solution

2. Sep 13, 2009

### Staff: Mentor

You didn't describe the problem completely, but I assume you're dealing with a two-disk velocity selector? The disks are moving at some angular speed omega?

If so, here's a hint: How much time does it take for a disk to move through the angle theta?