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[Solved] Force Diagrams Question

  1. Oct 9, 2008 #1
    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

    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. jcsd
  3. Oct 9, 2008 #2


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    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!
  4. Oct 9, 2008 #3
    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!
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