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A small block of mass m os takes slowly ...

A small block of mass m os takes slowly up a fixed hemisphere from `P` to `Q` and then slowly down along its surface from `Q` to `S` by force `F`, which at each point of the surface, is tangential to the surface. If the coefficient of friction is `mu`, then the work performed by the force `F` in taking the block from `P` to `S` along the hemispherical surface of radius `R` is :

A

`2mu mgR`

B

`mu mgR`

C

`pi mu mgR`

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
A
A small block …………
`W = int mu mg cos theta ds`
`W = overset(2R)underset(0)int mu mgdx`

`W = 2mu mg R`
Work done agasinst gravity is zero.
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