Rotational Motion: Supernova to Pulsar Transformation

[myoplex11]

Homework Statement

A supernova is the explosion of a large star. The progenitor, the star just before it explodes has a mass of 15 solar masses and a radius of 7*10^10m. After the supernova, a pulsar is left over. The pulsar has a mass of 2.2 solar masses and a radius of 10km.

a) If the pulsar rotates 75 times a second what is its angular velocity.
b) What was the angular velocity of the proginator.
c) What is the rotational kinetic energy of the pulsar.

Homework Equations

The Attempt at a Solution

is my work correct
a) angular velocity pulsar = (2pi * 75) / sec
b) would the angular velocity of the proginator be 0 i am not sure how to do this one.
c) K =.5*(2.2)*((10,000m)^2)

 

[LowlyPion]

I'd say in b) they are wanting you to calculate the angular momentum of the spinning pulsar given the final geometry and then apply that back to the geometry and mass of the proginator, relying on conservation of angular momentum.