Posted by **rosa** on Monday, November 11, 2013 at 11:22pm.

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 -
**Anonymous**, Tuesday, November 12, 2013 at 5:11am
4/3

- Physics Urgent please help -
**Damon**, Tuesday, November 12, 2013 at 8:14am
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 -
**rosa**, Tuesday, November 12, 2013 at 5:36pm
Thank you Damon

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