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Billiard ball collision at right angle

  1. Mar 18, 2009 #1
    1. The problem statement, all variables and given/known data
    Two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upward along the y axis at 2.0 m/s and ball B is moving to the right along the x axis with speed 3.7 m/s. After the collision (elastic), ball B is moving along the positive y axis. What is the final direction of ball A and what are their two speeds?

    2. Relevant equations
    mAvA + mBvB = mav'A + mBv'B
    1/2mAvA2 + 1/2mBvB2 = 1/2mAv'A2 + 1/2mBv'B2

    3. The attempt at a solution
    I know that because this is an elastic collision, momentum and kinetic energy are conserved. I think it's just that the two balls start on different axes is what's throwing me off.
  2. jcsd
  3. Mar 18, 2009 #2


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    Homework Helper

    Welcome to PF.

    Indeed the 2 dimensions do make a difference. You will want to treat them separately.

    Momentum in x is conserved
    Momentum in y is conserved
    KE is conserved.
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