Question

Suppose a star the size of our Sun (R0 = 695,500 km) rotates at a speed of 1.0 revolution every 12 days. If it were to undergo gravitational collapse to a neutron star of radius 11 km, what would its new rotation speed be? (rad/s)

Answer 1

In this ques, i would first like to tell that why would its angular speed increase...
so first of all,since the star is undergoing gravitational collapse,so its mass would remain constant,,Also there are no external forces acting on the system,as the gravitational collapse is due to mutual disturbance of the forces in the star..so only internal forces play the role here.
Hence the angular momentum should remain constant(i.e. I*W =const.)
..So all u got to do is to equate initial and final angular momentum..and u will get the answer..
please tell me if you found something wrong in my explanation..i wud like to rectify it..:)