physics
posted by donut .
A star with an initial radius of 1.0 x 10^8 m and period of 30.0 days collapses suddenly to a radius of 1.0 x 10^4 m. (a) Find the period of rotation after collapse. (b) Find the work done by gravity during the collapse if the mass of the star is 2.0 x 10^30 kg. (c) What is the speed of the person standing on the equator of the collapsed star? (Neglect any relativistic or thermal effects, and assume the star is spherical before and after it collapses.

Initial moment of inertia = (2/5)mass*R^2=(2/5)mass*10^16 initial angular velocity wi = 2pi /(30*60*60*24)
initial angular momentum =[(2/5)mass*10^16]*(2pi /(30*60*60*24))
final moment of inertia = (2/5)mass*R^2=(2/5)mass*10^8
final angular momentum= [(2/5)mass*10^8]wF
final angular velocity wf=?
wf = 242.406 rad / s
WF = 2PI / (T)
T= 0.026