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Homework Help: To what depth will the bullet penetrate the block in this case?

  1. Nov 30, 2008 #1
    1. The problem statement, all variables and given/known data
    A 7.00 g bullet, when fired from a gun into a 1.00 kg block of wood held in a vise, penetrates the block to a depth of 7.60 cm. This block of wood is next placed on a frictionless horizontal surface, and a second 7.00 g bullet is fired from the gun into the block. To what depth will the bullet penetrate the block in this case?

    2. Relevant equations
    m1v1 + m2v2 = (m1+m2)vf

    3. The attempt at a solution
    I have no clue how to solve this problem. I don't really know what to do with the depth of penetration by the bullet. Can anyone please help?
  2. jcsd
  3. Dec 1, 2008 #2


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    Science Advisor
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    Gold Member

    Re: collision

    There's a significant loss of KE in part 1....like all of it, 1/2mv_b^2. In part 2 , apply conservation of momentum, and determine the total loss of KE. It' ll be a bit less; how does that ratio difference relate to the new depth of penetration?
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