Calculating Force in a Rifle-Bullet System

[*intheclouds*]

Homework Statement

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?

Homework Equations

F=MA
w=mg
v=v₀+at
v²=v₀²+2ax

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 don't 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!

 

[berkeman]

Homework Statement

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?

Homework Equations

F=MA
w=mg
v=v₀+at
v²=v₀²+2ax

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 don't 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!

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!

 

[*intheclouds*]

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!