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neeru . Grade: 11

MI  of a  ring is mr^2.

If  we  treat rings as  elements of a disc as well as of a hemisphere,then MI of   a disc and of hemisphere should be  same (becoz mass  as well as perp. distance of  every corresponding ring in both from  the axis will be same , but  actually  not. What is wrong in the concept?

           (here  axis  is the axis passing through centre and perp. to plane in both cases)

8 years ago

Answers : (1)

Badiuddin askIITians.ismu Expert
147 Points

Dear neeru

it is because of that for same mass and radius surface area of disk and hemisphear is not same

for disk we right =dm = (M/πR2 ) 2πrdr

and for the hemisphear =dm = (M/2πR2) (2πRsinΘ)(RdΘ)

here we should consider that in case of dish ,element area is a area of ring which is  a plane surface

but in case of hemisphear element area is not plane urface it is a curved surface.

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8 years ago
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