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Homework Help: Amount of energy lost to friction due to change in rotational inertia

  1. Apr 2, 2014 #1
    1. The problem statement, all variables and given/known data

    A 2.8-m-diameter merry-go-round with rotational inertia 140kg⋅m2 is spinning freely at 0.40rev/s . Four 25-kg children sit suddenly on the edge of the merry-go-round.

    a) Find the new angular speed.

    b) Determine the total energy lost to friction between the children and the merry-go-round.
    3. The attempt at a solution

    a) 0.17rev (verified)

    b) The old mass is 17.85714286kg, old angular speed is 2.513274123 ms-1
    The new mass is 117.85714286kg, new angular speed is 1.066237507ms-1

    To find the change in energy:

    0.5(117.85714286kg)(1.066237507ms-1)2 - 0.5(17.85714286kg)(2.513274123 ms-1)2

    The answer is 260j but I'm not getting it.
  2. jcsd
  3. Apr 2, 2014 #2
    Managed to solve it. I made a slip. It was 2.8m diameter instead of 2.8meter radius.:devil:
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