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Homework Help: Momentum and motion question

  1. Oct 21, 2007 #1
    First post here on the forum, so excuse me for any mistakes.

    A bullet of mass m is fired into a block of mass M initially at rest at the edge of a frictionless table of height h. The vullet remains in the block, and after impact the block lands a distance d from the bottom of the table. Determine the initial speed of the bullet.

    No variables are given, the answer should be in the form of an equation.

    I'm having a really hard time starting this problem, but am pretty confident that with a hint I could get it taken care of. I'm thinking that the conservation of momentum equation (Pi=Pf) will help determine the velocity of the bullet, but I'm not sure how to compensate for the block falling off of the desk. Maybe the laws of motion equation? (X=Xi+VixT+1/2AT^2)?

    Any help would be appreciated. I have the answer from the book, but am not sure how to figure it out. Let me know if knowing the answer would help. Thanks
  2. jcsd
  3. Oct 21, 2007 #2
    You're absolutely right. Use the x equation to find the initial velocity of M and m (when they are together). Then relate that velocity to the initial velocity of the bullet before it hits the block. Is there a specific place where you have trouble? Don't forget that you have to consider the motion in the horizontal and vertical directions as the block and bullet are falling off the table.
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