# Homework Help: Help on homework please force

1. Oct 24, 2007

### eb41490

help on homework please....force

hey, i dont know if what i did for this question is correct, because the equation i found in my textbook may not be the right one to use.

A 5.0g bullet leaves the muzzle of a rifle with a speed of 320m/s. What force (assumed constant) is exerted on the bullet while it is traveling down the .82m-long barrel of the rifle?

i used the equation:
(m(v^2)) / 2d =F

(.005kg*(320m/s)^2 )/ (2*.82m) =F
F= 312.2N

Is this close to being correct?

2. Oct 24, 2007

### BerryBoy

There are two ways to do this problem, the easiest is with energy (which is what I assume you did), I deleted a post doing the other way

Take work done on the bullet and equate to kinetic energy:

$$Fd = \frac{1}{2}mv^2$$
$$F = \frac{mv^2}{2d}$$

Your answer looks good to me

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