Mass per unit area of a disc of inner radius `'a'` and outer radius `'b'` is given by `((sigma_(0))/(r)),r` distance from center. Its radius of gyration `w.r.t.` axis of rotation passing through center and perpendicular to plane is

Options

A. `sqrt((B^(4)-a^(4))/(3(b^(2)-a^(2))))`
B. `sqrt((b^(3)-a^(3))/(3(b-a)))`
C. `sqrt((b^(3)-a^(3))/(5(b-a)))`
D. `sqrt((b^(4)-a^(4))/(5(b^(2)-a^(2)))`

Answer

B