# Ratios of Initial to Final Energy/Momentum/Velocity

## Homework Statement

A rotating star collapses under the influence of gravitational forces to form a pulsar. The radius of the star after collapse is 4.00 10-4 times the radius before collapse. There is no change in mass. In both cases the mass of the star is uniformly distributed in a spherical shape.
(a) What is the ratio of the angular momentum of the star after collapse to before collapse?

(b) What is the ratio of the angular velocity of the star after collapse to before collapse?

(c) What is the ratio of the rotational kinetic energy of the star after collapse to before collapse?

(d) If the period of the star's rotation before collapse is 5.00 107 s, what is its period after collapse?
____ s

## The Attempt at a Solution

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