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Homework Help: Ballistics Momentum problem

  1. Mar 29, 2010 #1
    In a ballistics test, a 25.0g bullet traveling horizontally at 1100m/s goes through a 40.0cm -thick 250kg stationary target and emerges with a speed of 900m/s . The target is free to slide on a smooth horizontal surface.

    the 1st question of this problem ask: How long is the bullet in the target?

    I simply do:

    40.0cm=0.4m ; 0.4m/(900m/s)=4.4*10^-4

    The answer shows 4.0*10^-4

    Did I make a mistake or it is just a rounding problem?
     
  2. jcsd
  3. Mar 30, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi ZzZerozZ! Welcome to PF! :smile:

    i] in your distance/speed, you've used the width of the block as the distance, but the block is moving, so the distance is longer

    ii] your speed is the final speed, so it's too small :redface:
     
  4. Mar 30, 2010 #3
    Using s = (u+v)/2 *t the answer is 4 *10^-4. s= distance, u = inital vel, v= final vel.
     
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