Posted by rosa on .
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,
4/3

Physics Urgent please help 
Damon,
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,
Thank you Damon