Angular Momentum: Solving Homework Confusion

[Litcyb]

Homework Statement

I am just confused about Angular momentum.

Homework Equations

KE(rotational)= 1/2Iw^2
Angular momentum= Iw

The Attempt at a Solution

Why can I do the change in KE rotational to calculate the her final angular velocity in 3 revs?
very confused! :( both equations relate to moment of inertia and angular velocity.

Homework Statement

Homework Equations

The Attempt at a Solution

 

[Doc Al]

Only angular momentum is conserved here. That's all you need.