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Angular Momentum of a turntable with frictionless bearings

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    You are standing on the edge of a turntable with frictionless bearings. It is initially rotating when you catch a ball, which is moving in the same direction but faster than you are moving and on a line tangent to the edge of the turntable. Assume you do not move relative to the turntable.

    (a) Does the angular speed of the turntable increase, decrease or remain the same during the catch?
    I know this increases

    (b) Does the magnitude of your angular momentum (about the rotation axis of the turntable) increase, decrease, or remain the same during the catch?
    I know this increases as well

    (c) How does the ball's angular momentum (about the rotation axis of the table) change after the catch? Increase, decrease, or remain the same?
    This decreases (ball comes to a stop)

    (d) How does the total angular momentum of the system, you-table-ball (above the rotation axis of the turntable), change after the catch? Increase, decrease, or remain the same?
    Without actual numbers, I am having trouble trying to figure this one out in my head. Any ideas?



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 23, 2010 #2
    (c) You are right that it decreases, but the ball didn't come to a full stop. It is now travelling with you around in a circle.

    (d) Don't forget that the total angular momentum is conserved.
     
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