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Homework Help: Elastic Glancing Collision

  1. Nov 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Two masses (m and 3m) are moving towards each other along the x-axis with the same initial speed (v). Mass m is travelling to the left while mass 3m is travelling to the right. They undergo elastic glancing collision such that mass m is moving downwards after the collision at right angles from its initial direction. a) Find the final speed of the two masses and b) The angle at which the 3m mass is scattered.

    2. Relevant equations

    3. The attempt at a solution
    Pi=pf (x-direction)
    3mv-mv = 3mv
    2mv = 3mv

    pi = pf (y-direction)
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 9, 2012 #2


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    Homework Helper

    3mv-mv = (3m)*Vx where Vx is the velocity of 3m in the x direction after collision
    2mv = 3mv*Vx
    Vx = (2/3)*v

    Oh, I made that mistake, too! But you can't use "v" for the downward speed of mass m after the collision as that letter is used for something else. Use another letter, perhaps "u". And Vy for the upward speed of 3m. Then you see that the equation can't be solved since you have two unknowns, u and Vy.

    You can get another equation from the fact that the collision is elastic. That should be delightfully complicated.
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