Physics Urgent please help

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A figure skater stands on one spot on the ice(assumed frictionless) and spins around with her arms extended. When she pulls in her arms, her moment of inertia decreases to 3/4 of the initial value. Assume that her spin angular momentum is conserved. What is the ratio of her final rotational kinetic energy to her initial rotational kinetic energy?

  • Physics Urgent please help -

    4/3

  • Physics Urgent please help -

    I omega, angular momentum, does not change so:
    I1 omega1 = I2 omega2

    I1 omega1 = (3/4) I1 omega2
    so
    omega2 = omega 1 * 4/3
    then
    original ke = (1/2) I1 omega1&2
    final Ke = (1/2) I2 omega2^2
    so
    final Ke=(1/2)(3/4)I1 *(4/3)^2 omega1^2
    = 4/3 of original
    (she had to do work to pull her arms in)

  • Physics Urgent please help -

    Thank you Damon

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