# Homework Help: Finding force(N) wood has against the bullet

1. Oct 1, 2011

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

22.0-caliber rifle bullet of mass 1.80 g, traveling at 320 m/s strikes a block of soft wood, which it penetrates to a depth of 0.140 m. The block of wood is clamped in place and doesn't move. Assume a constant retarding force.

What force, in newtons, does the wood exert on the bullet?

2. Relevant equations

3. The attempt at a solution

Long story short, acceleration is -365714.29 m/s^2

Is it really as simple as .0018*-365714.29 = -658.29 N ? Or maybe 658.29 N since the force of the wood on the bullet is opposite of the bullet on the wood?

Since Fnet = ma

Last edited: Oct 1, 2011
2. Oct 1, 2011

### PeterO

It is that simple [I hope you a value is correct; I haven't checked]

The question referred to a retarding force, so easiest just to answer "The retarding force is 658N" watch the significant figures in your final answer - you use all the figures i your calculations]

3. Oct 1, 2011

### Andrew Mason

You might find it easier to use energy: the work done by the wood on the bullet is equal to the loss of kinetic energy. So:

$$F = KE/d$$

AM

4. Oct 1, 2011