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Rotational kinetic energy and moment of inertia

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data

    A 16 g CD with a radius of 6.0 cm rotates with an angular speed of 42 rad/s.
    (a) What is its kinetic energy?

    2. Relevant equations

    k=1/2Iw^2

    3. The attempt at a solution
    k=1/2(0.016x0.0036)(1764)=0.05 J
     
  2. jcsd
  3. Dec 3, 2009 #2

    ideasrule

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    Careful. The moment of inertia of a disk is not MR^2. That's the moment of inertia for a hoop, or for a point mass.
     
  4. Dec 3, 2009 #3
    ohhh so should i have 1/2mr^2
     
  5. Dec 3, 2009 #4

    ideasrule

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  6. Dec 3, 2009 #5
    kk sweet thanks! i got it right :)
     
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