Rotating gas cloud A cloud of interstellar gas of total mass M can move freely in space. Initially the cloud has the form of a uniform sphere of radius a rotating with angular speed about an axis through its centre.
Later, the cloud is observed to have changed its form to that of a thin uniform circular disk of radius b which is rotating about an axis through its centre and perpendicular to its plane. Find the angular speed of the disk and the increase in the kinetic energy of the cloud.