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Need help with Momentum and Collisions

  1. Jan 7, 2007 #1
    Need help solving this problem
    [​IMG]

    Thank you
     
  2. jcsd
  3. Jan 7, 2007 #2

    cristo

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    Hi, and welcome to PF. Please give your thoughts on the question, before we can help. Better still, use the posting template with which you were provided!
     
  4. Jan 7, 2007 #3
    What is the momentum before the block is released? How about after? Then you can use energy for the second part
     
  5. Jan 7, 2007 #4
    the momentum before the release is 0, and after is 2. I understand that i need to apply conservation of momentum in this problem somehow, but I dont see a way so far.
     
  6. Jan 7, 2007 #5

    cristo

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    Conservation of mmtm states that mmtm before=mmtm after. Think of the total system. Before the block starts moving, like you said, pi=0. When the block hits the horizontal surface, the total momentum pf= 0.5*4-v2*m2. (The negative sign appears, since the block moves to the left.) From this you can find the velocity of the wedge.

    Can you carry on from here?
     
    Last edited: Jan 7, 2007
  7. Jan 7, 2007 #6
    v2 = 2/3 m/s ( to the left) ?

    and for part b, should I use convservation of energy (potential and kinetic) in order to find the height?
     
  8. Jan 7, 2007 #7

    cristo

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    I've not checked you calculation, but yes, it's to the left.

    For b, as you say, you should use conservation of energy.
     
  9. Jan 7, 2007 #8
    thank you very much for your help :smile:
     
  10. Jan 7, 2007 #9

    cristo

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    You're very welcome! :smile:
     
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