# Speed of A Bullet

1. Oct 4, 2005

### quicknote

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.

The picture can be found here.

http://ca.geocities.com/canbball/MRB_rr_8_a.jpg [Broken]

I know that v = (delta)D/(delta)T where D is distance and T is the period.
But I'm not sure how to find the ratio between the angle and the measure of a full revolution.
Any help would be much appreciated!

Last edited by a moderator: May 2, 2017
2. Oct 4, 2005

### Integral

Staff Emeritus
your equation
$$v = \frac {\Delta D} {\Delta T}$$
Cannot be correct. Both D and T are constants of your problem, so do not change.

You need to start with

$$v= \frac D t$$
where t is the time required to travel the distance between the disks. You are given that it take T secs to do a complete rotation, what is that in terms of Pi?

your goal is to find an expression for t involving T and $\Theta$.

Last edited by a moderator: May 2, 2017
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