# Homework Help: Skater Rate of Rotation

1. Nov 15, 2009

### Devin Longo

1. The problem statement, all variables and given/known data

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

2. Relevant equations

?

3. 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!

2. Nov 15, 2009

### Delphi51

angular momentum before = angular momentum after

3. Nov 15, 2009

### Devin Longo

I still don't really understand

4. Nov 15, 2009

### 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.