An ice skater can rotate about a vertical axis with an angular velocity Wo by holding her arms straight out. When she pulls her arms close to her, her angular velocity becomes 2 w0, without any extra torque. What is the ratio of her final rotational KE to her initial rotational KE?

Question

youngster · Answer

Why is the ratio 2 instead of 4?
since the equation for rotational KE is
$$KE=1/2  I   \omega _{0}^{2}$$

mrdoe · Answer

you mean the ratio of the angular velocity (omega) right?

vincent-lyon.fr · Answer

Because, as she brings her arms in, she changes shape and her moment of inertia is changing too.
Work out new expression of moment of inertia from conservation of angular momentum, and it's done.

koikkara · Answer

hey that`s not 2...it`s half(1/2)

shubhamsrg · Answer

yep..due to 0 net torque , angular momentum is conserved
USE THIS FACT//