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Two discs cone of density 7200 kg//m^(3)...

Two discs cone of density 7200 `kg//m^(3)` and another of density `9000km//m^(3)` have the same mass and thickness. What is the ratio of their moments of inertia?

A

`(4)/(5)`

B

`(5)/(4)`

C

`(5)/(9)`

D

`(1)/(9xx7.2)`

Text Solution

Verified by Experts

The correct Answer is:
B
`because M_(1)=M_(2)" "therefore v_(1)rho_(1)=v_(2)rho_(2)`
`therefore piR_(1)^(2)h rho_(1)=piR_(2)^(2)h rho_(2)`
`therefore" "(R_(1)^(2))/(R_(2)^(2))=(rho_(2))/(rho_(1))" …(1)"`
`therefore" "(I_(1))/(I_(2))=((1)/(2)MR_(1)^(2))/((1)/(2)MR_(2)^(2))=(R_(1)^(2))/(R_(2)^(2))=(rho_(2))/(rho_(1))=(9000)/(7200)=(5)/(4)`
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