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Homework Help: Looking for verification on a momentum & collision problem

  1. Jun 13, 2006 #1
    Here is the problem:
    Runner1 is going 20 degrees NofE with a mass of 60kg and v=5m/s. Runner2 is going 20 degrees NofW with a mass of 80kg and v=4m/s when they collide. What are their respective momentums prior to the collision? What is their final velocity and direction after collision if it was perfectly inelastic collision?

    For question1 I got L=300kgm/s for runner1 and L=-320kgm/s for runner2.

    For question2 I'm a little perplexed. This is what I did.
    (x) m1v1+m2v2=(m1+m2)vf
    -4sin20(80kg)+5sin20(60kg)=(60kg+80kg)vf
    -109+103=140vf
    -6=140vfx
    vf(x)=-.049m/s

    (y) m1v1+m2v2=(m1+m2)vf
    4cos20(80kg)+5cos20(60kg)=(60kg+80kg)vf
    301+282=140vf
    583=140vf
    vf(y)=4.16m/s

    Then I took the TAN-1(4.16/-.049) to find theta and it gave me -89degrees North of East.

    Does this look right?

    Thank you to anyone who can give me some insight. I appreciate your help.
     
  2. jcsd
  3. Jun 14, 2006 #2
    Your method is right.
    But your vector algebra is slightly flawed.
    For (x) take cosine and not sine.
    Viceversa for (y) .
     
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