Conservation of Angular Momentum A collapsing Star

[dsmwc8]

1. After a collapsing star decreases its radius to half its initial size, predict what will happen to its angular velocity(Assume uniform density at all times)Your answer describes the high angular speed of neutron stars. Find the change in the rotational kinetic energy of the star. Where does the energy come from?



I=2/5MR^2 I think the energy comes from the force of the stars own gravity,

I also thought that the angular velocity would increase but I don't know how to find the change in kinetic energy. Any clear explanation would be great, I think I am on the right track but need a little help.

The Attempt at a Solution

 

[Dick]

You are completely correct about the source of the energy. Find the change in angular velocity using conservation of angular momentum. Use the change in angular velocity to find the change in rotational kinetic energy.