Question

A disc of radius R and thickness R÷6 has moment of inertia I about an axis passing through its centre and perpendicular to its plane . Disc is melted and recast into a solid sphere. The moment of inertia of a sphere about its diameter is

Answer 1

volumedisk=volumesphere
PI*R^3/6=4/3 PI r^3
r=R/2
Isphere=.40 MR^2
Idisk=1/2 Mr^2= .50 MR^2/4=.125 MR^2

so the sphere has a moment about .40/.125 greater