Q: A solid sphere of mass M, radius R and having moment of inertia about an axis passing through of centre of mass as I, is recast into a disc of thickness t, whose moment of inertia about an axis passing through its edge and perpendicular to its plane remains I. then, radius of the disc will be

(a) $\frac{2 R}{\sqrt{15}}$

(b) $ R \sqrt{\frac{2}{15}}$

(c) $\frac{4 R}{\sqrt{15}}$

(d) $\frac{R}{4}$

Ans: (a)