An extremely dense neutron star with mass equal to that of the Sun has a radius of about 10 km −about the size of Manhattan Island. These stars are thought to rotate once about their axis every 0.03 to 4 s, depending on their size and mass. Suppose that the neutron star described in the first sentence rotates once every 0.040 s

Question

If the volume of the neutron star then expanded to occupy a uniform sphere of radius 1.4×108m (most of the Sun's mass is in a sphere of this size) with no change in mass or rotational momentum, what time interval would be required for one rotation? By comparison, the Sun rotates once about its axis each month.

Answer 1

Use conservation of momentum to solve this.