If two circular discs A and B are of same mass but of radii rand 2r respectively, then the moment of inertia of A is [Kerala CEE 2015]

Given, radius of circular disc  A,r1=rRadius of circular disc  B,r2=2rFor disc  A,IA=mr2               …(i)For disc  B, IB=m(2r)2=4mr2     …(ii)On dividing Eq. (i) by Eq. (ii), we get∴ IAIB=mr24mr2⇒IAIB=14⇒IA=14IBSo, moment of inertia of A is one-fourth that of B.