A coin of mass m and radius r having moment of inertia I about the axis passing through its centre and perpendicular to its plane. It is beaten uniformly to form a disc of radius 2r. What will be the moment of inertia about the same axis?

Options

A. I
B. 2I
C. 4 I
D. 16 I

Answer

C

Explanation

Moment of inertia of coin of mass m and radius r about the axis passing through its centre and perpendicular to its plane is
`I = (mr^2)/(2) " " … (i)`
Moment of inertia of formed disc about the same axis is `I. = (m(2r)^(2))/(2) = 4 ((mr^(2))/(2)) = 4I " "` (Using (i))