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Homework Help: A Mass on a Turntable: Conceptual

  1. Sep 21, 2007 #1
    1. The problem statement, all variables and given/known data
    A small metal cylinder rests on a circular turntable that is rotating at a constant rate. Let R be the distance between the cylinder and the center of the turntable. Now assume that the cylinder is moved to a new location R/2 from the center of the turntable. Which of the following statements accurately describe the motion of the cylinder at the new location?

    A The speed of the cylinder has decreased.
    B The speed of the cylinder has increased.
    C The magnitude of the acceleration of the cylinder has decreased.
    D The magnitude of the acceleration of the cylinder has increased.
    E The speed and the acceleration of the cylinder have not changed.

    There could be more than one answers.

    2. Relevant equations


    3. The attempt at a solution

    So I tried out this experiment. It moves at a constant motion around the center of the mass and the speed is constant. Since it says "R/2" I decresaed the radius and the speed increases. So I think B is one of the answers. What else should I be aware of?
    Last edited: Sep 21, 2007
  2. jcsd
  3. Sep 21, 2007 #2


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    I don't see why the speed would increase... if [tex]\omega[/tex] the rate of rotation of the turntable is the same... then the speed of the cylinder is [tex]R\omega[/tex] where R is the radius... so a smaller radius implies smaller speed... unless I'm missing something...

    I'm thinking the cylinder won't rotate about its own axis if it's placed initially at rest on the turntable... because the rotation of the turntable only imparts angular momentum about the vertical axis... the axis of the cylinder is perpendicular to the vertical axis...
  4. Sep 21, 2007 #3
    Oh, i see. I misinterpretted the problem. Thanks for the reply.
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