Question

A solid sphere of mass M and radius R is divided into two unequal parts. The first part has a mass of 7M/8 and is converted into a uniform disc of radius 2R. The second part is converted into a uniform solid sphere. Let I₁ be the moment of inertia of the disc about its axis and I₂ be the moment of inertia of the new sphere about its axis. The ratio I₁/I₂ is given by:

(1) 65 (2) 140 (3) 185 (4) 285 

Answer 1

Disc :

Idisc = \(\frac{7M}{8}\times\frac{(2R)^2}{2}=I_1\)

Solid sphere :

\(\frac{R}{2}\) = r = radius of the solid sphere