Determining New Angular Velocity

[crushedcorn]

Homework Statement

A star with mass 2.4x10³⁰ kg and diameter 1.7x10⁹ m rotates once every 34 Earth days. It eventually dies and becomes a white dwarf, shedding about half of its mass and contracting to a diameter of 1.9x10⁸ m. If we approximate the star as a perfect sphere, what is its resulting angular velocity?

Initial star r = 8.5x10⁸ m
Initial star m = 2.4x10³⁰ kg
Initial star ω = 1 rev/34 days = 1.85x10⁷ rad/s
White dwarf r = 9.5x10⁷ m

Homework Equations

I=(2/5)MR²

The Attempt at a Solution

I'm getting really stuck on this one. I can determine I for the initial star (I=(2/5)(2.4x10³⁰ kg)(8.5x10⁸)² m=6.94x10⁴⁷ kgxm², but from there I'm not sure where to go. I'm not even sure if that's relevant. I'm not looking for a handout here, but any guidance would be appreciated!

 

[paisiello2]

Why do you need to know I?

 

[sun18]

There are no external torques in this problem, therefore angular momentum is conserved.

h = Iω

 

[paisiello2]

Yes, so can you write an equation that shows this?

 

[haruspex]

There are no external torques in this problem, therefore angular momentum is conserved.

h = Iω

Yes, but be careful. What do you think the angular momentum of the shed mass will be at the end?