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Homework Help: Need help in the physic HW question!

  1. Oct 22, 2012 #1
    1. The problem statement, all variables and given/known data

    A bullet of mass m = 17.6 g traveling horizontally at speed vo = 565 m/s strikes a block of mass M = 678 g sitting on a frictionless, horizontal table. This time, however, it comes out the other side of the block at speed v = 524 m/s.

    Calculate J, the magnitude of the impulse exerted by the bullet on the block.

    2. Relevant equations


    Impulse = Momentum = Ft = mv_f - mv_i

    3. The attempt at a solution

    I think that the impulse is same as the momentum. I think that is...

    Impulse = mv_f - mv_i

    I got -0.722 but it's incorrect. My professor said that impulse can't be negative because time is positive and force is positive.

    But it seems like I'm on the wrong path. (This is from the previous question. Seems like nobody wants to pay attention, so I ask again.)
  2. jcsd
  3. Oct 22, 2012 #2
    Impulse is the change in momentum during a collision. But the question's asking for the impulse on the bullet by the block, not the other way around. So you'll have to find the change in momentum of the block first.
  4. Oct 22, 2012 #3


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    This is the impulse exerted on the bullet by the block.
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