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I Force acting on the center of mass of a rolling disk

  1. Jun 17, 2017 #1
    Hello. The following situation I thought out confuses me so I am wondering where my mistake lies.
    A uniform disk of mass M and radius R sits on its edge. A string is attached to the highest point and pulled with a Force F in the x direction.

    The moment of inertia of the disk is MR^2/2 making the angular momentum about the center of mass MR^2w/2 where w is the angular velocity. The torque about the center of mass seems to be FR. Since torque is the derivative of angular momentum we have FR=MR^2a/2 where a is the angular acceleration.
    This means the angular acceleration is equal to 2F/RM. The acceleration A of the c.o.m is equal to aR, so it is equal to 2F/M, making the force acting on the body equal to 2F/M*M= 2F???
  2. jcsd
  3. Jun 17, 2017 #2


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    Science Advisor

    What makes you say that the acceleration of the center of mass is equal to aR? Nobody said that the disk was rolling without slipping.
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