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Homework Help: Gun shot question

  1. May 8, 2008 #1
    1. The problem statement, all variables and given/known data
    A rifle is held rigidly by a supporting test frame. When fired horizontallly, a 50 g bullet attains a muzzle exit velocity of 500 m/s if it takes 0.003 s for the bullet to travel the length of the barrel, determine the average horizontal force applied to the gun by the test frame during firing.

    2. Relevant equations

    3. The attempt at a solution

    I know that the answer is 8.33 kN but I do not know how to solve it.
    I think that we evaluate the forces on the x axis, there are no forces on the y axis but
    i am not sure, any help?
  2. jcsd
  3. May 8, 2008 #2


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    Hint: 8330 is half of 50/.003.
  4. May 8, 2008 #3
    lol, so i multiply 50/0.3 by a half? Thanks for the help but can you tell me what steps i should take, i really do not get this problem.
  5. May 8, 2008 #4
    F = ma

    With what you're given, how can you find the acceleration?

    You have the mass, but you have to change it's units so you can get the force in newtons (N).
  6. May 9, 2008 #5


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    (i must admit i think it's a badly-worded question, and i don't really understand the mechanical set-up :frown: … but what they obviously want is …)

    ok … Newton's second law …
    force = mass times acceleration​
    so …
    average force = mass times average acceleration …​

    and average acceleration is … ? :smile:
  7. May 9, 2008 #6
    In order to find the average force we need to know the average acceleration,to find the average acceleration we divide 500/0.003, which is velocity divided by time. This comes out to be 166666.667., then we multuply by 50, correct? I`m sorry if i am wrong but I am really trying to answer this based on the help you are giving me, do we find average acceleration by a different method?
  8. May 9, 2008 #7


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    No … 1 N = 1 kg m /s² … so we multiply by 0.05. :smile:
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