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Homework Help: Gun, shell question.

  1. Mar 1, 2008 #1
    1. The problem statement, all variables and given/known data
    A gun of mass 500Kg fires a shell of mass 2Kg with a muzzle velocity of 500m/s.
    Calculate:
    i) the velocity of recoil of the gun
    ii) the force required to stop the gun in a distance of 0.25m


    2. Relevant equations



    3. The attempt at a solution
    i)I got the velocity of the gun by using the principal of conservation of momentum:
    (500)(0) + (2)(0) = 500v + (500)(2). I got 2m/s.

    ii)First i used v=d/t, 2=0.25/t, I got 0.125 seconds.
    Then i used Force = change in momentum/time taken.
    I get 8000N but the book says 4000N.
    Im not sure what im doing wrong??
     
  2. jcsd
  3. Mar 1, 2008 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi milan!

    You've assumed the velocity is constant (at 2 m/sec).

    That gave you the wrong value of t.

    Can you see some other way to calculate t (from initial velocity, final velocity, and distance)? :smile:
     
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