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Homework Help: How much rotational kinetic energy does the disk have ?

  1. Mar 16, 2012 #1
    A string is wrapped around a disk of mass 2.1 kg (it's density doesn't have to be uniform). From rest, you pull the string with a constant force of 9 N. At this instant, the center of mass has moved 0.11 m, and your hand has moved 0.28 m.

    1. At this instant, how much rotational kinetic energy does the disk have relative to its center of mass?

    2. At this instant, the angular speed of the disk is 7.5 rads/s. What is the moment of inertia of the disk?
  2. jcsd
  3. Mar 16, 2012 #2


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    Staff: Mentor

    Relevant equations? Attempt at solution? Your thoughts?
  4. Mar 16, 2012 #3


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    Gold Member

    Exactly what is meant by rotational kinetic energy "relative to the center of mass"?
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