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Homework Help: Rotational Motion+Gravity

  1. May 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A 25gm mass sits on the surface of a circular disk 10 cm from the center of the disk. The force of static frictio nbetween the mass and surface of the disk is 0.075 N. The disk is initially at rest, but then experiences a constant angular acceleration of 0.80 rad/s^2. How many revolutions will the disk make before the mass starts to slip outward?

    2. Relevant equations
    i'm not exactly sure what equation to use-which is why i'm here...

    3. The attempt at a solution
    (.80rad) (1 rev) ....= 1.3rev/s

    i dont know ehre to go from here...
  2. jcsd
  3. May 5, 2009 #2


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    Homework Helper

    Consider the centripetal acceleration on the mass. At what ω then will the centripetal force on the mass overcome the friction that maintains it in position?

    Once you know ω, you can then determine the angular displacement.

    Maybe this link would be helpful:
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