# [Solved] Force Diagrams Question

1. Oct 9, 2008

### *intheclouds*

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

A rifle weighs 50.0 N, and its barrel is 0.750 m long. It shoots a 25.0 g bullet, which leaves the barrel at a speed (muzzle velocity) of 320 m/s after being uniformly accelerated. What is the magnitude of the force exerted on the rifle by the bullet?

2. Relevant equations
F=MA
w=mg
v=v0+at
v2=v02+2ax

3. The attempt at a solution
I wasn't totally sure of what I was doing, but this is what I did:
I used the equation: v2=v02+2ax and did-- 3202=0+2(a)(.750) and I got 68266.67 m/s2. I dont know if I did this right, or if I even used the right equation.

Then I used the F=MA equation. F=.25(68266.67) to get 17067 N, but when I typed in that answer to Webassign, it was wrong.

Any help would be greatly apprecitated. Thank you!

2. Oct 9, 2008

### Staff: Mentor

Re: Force Diagrams Question

Check your units on what I bolded in your post. It's good to write out the units of each quantity in your equations, to make sure you don't make mixed-units errors like this. I've found that habit of carrying along units in my calculations to be a huge help.

Welcome to the PF!

3. Oct 9, 2008

### *intheclouds*

Re: Force Diagrams Question

That worked! Thank you so much! You are amazing! =]
I generally get the concepts, but then I make silly little mistakes like that and I can't find where I went wrong.

And thanks for the welcoming!