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Total kinetic energy for rolling hoop

  1. Dec 5, 2015 #1
    1. The problem statement, all variables and given/known data
    A hoop has a mass of 200g and a radius of 25cm (ICM = MR2 ). It rolls without sliding along level ground at VCM = 5m/s. What is it's total kinetic energy?

    2. Relevant equations
    K = 1/2Iω2
    ICM = MR2
    v = rω

    3. The attempt at a solution
    The answer is 5J, but I'm getting 2.5J.

    ICM = MR2 = (0.2)(0.25)(0.25) 0.0125
    ω = v / r = 5/0.25 = 20

    K = 1/2(0.0125)(20)2 = 2.5J

    Am I omitting something from the total kinetic energy equation?
  2. jcsd
  3. Dec 5, 2015 #2
    You should consider translational motion too.
  4. Dec 5, 2015 #3
    Thanks! I forgot that a rolling object experiences both translational AND rotational motion. D'oh!
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