Two discs of the same material and thickness have radii 0.2 m and 0.6 m. Their moments of inertia about their axes will be in the ratio of

Options

A. `1:81`
B. `1:27`
C. `1:9`
D. `1:3`

Answer

A

Explanation

`I=(1)/(2)MR^(2)=(1)/(2)` (volume `xx` density) `xx R^(2)`
= `(1)/(2)(piR^(2)xxtxxrho)R^(2)`
`IpropR^(4)` ( As t and `rho` are same )
`(I_(1))/(I_(2))=((R_(1))/(R_(2)))^(4)=((0.2)/(0.6))^(4)=(1)/(81)`