Two thin uniform rings made of same material and of radii `R` and `4 R` are joined as shown. The mass of smaller ring is `m`. Find the `M.I.` about an axis passing through the center of mass of system of rings and perpendicular to the plane.

Options

A. `85mR^(2)`
B. `90mR^(2)`
C. `70mR^(2)`
D. `35mR^(2)`

Answer

B

Explanation

`l=l_("larger")+l_("smaller")`
`l=4M(4R)^(2)+[MR^(2)+M(5R)^(2)]90MR^(2)`.