Explanation:
It is given that, a solid metal sphere of diameter D is spinning in a gravity-free region of space with an angular velocity of ω.The sphere is slowly heated until it reaches its melting temperature, at which point it flattens into a uniform disk of thickness D/2.
The angular momentum remains conserved in this case. The relation between the angular momentum and the angular velocity is given by :

Where
are moment of inertia of sphere and the disk respectively
Here, volume before = volume after


Initial angular momentum,

..........(1)
Final angular momentum,

............(2)
From equation (1) and (2) :


Hence, this is the required solution.