# Homework Help: Angular Momentum/Velocity HW Help

1. Aug 1, 2012

### Parzival

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

A device can be used to measure the speed of a bullet. The device consists of two rotating disks, separated by a distance of d = 0.850 m, and rotating with an angular speed of 95.0 rad/s. The bullet first passes through the left disk and then through the right disk. It is found that the angular displacement between the two bullet holes is 0.240 rad. From these data, determine the speed of the bullet.

2. Relevant equations

Angular velocity = angular displacement/time
3. The attempt at a solution
I attempted to set up an equation, but I simply couldn't.

Last edited: Aug 1, 2012
2. Aug 1, 2012

### voko

What is the angular displacement of the first disk during the bullet's flight between the disk? Of the second one?

3. Aug 1, 2012

### CWatters

The definition of Velocity is distance/time

The distance is known so you just need to work out the time it takes to travel the distance between the discs.

The definition of angular velocity is

Angular velocity = angle/time

So rearrange that to give an equation for the time. Plug that into the first equation.

4. Aug 1, 2012

### Parzival

Please clarify? I've been stumped for a long time.