Conservation of Angular Momentum in Skater's Spin Rate Change

[Devin Longo]

Homework Statement

A figure skater is spinning at a rate of 2 rev/s with her arms outstretched. She then draws her arms into her chest, reducing her rotational inertia to 61% of its original value. What is her new rate of rotation?

Homework Equations

?

The Attempt at a Solution

w/2 = 1/sqrt(0.61)
w = 2.56 rev/s

This isn't correct according to the website, can someobody help me with a better equation and how to solve this one?

Thanks!

 

[Delphi51]

angular momentum before = angular momentum after

 

[Devin Longo]

I still don't really understand

 

[Delphi51]

Angular momentum is conserved; it stays the same unless there is an external torque. So
angular momentum before = angular momentum after

You need to write the formula for angular momentum on both sides. Fill in the quantities you know and solve for the one you want to find.