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A cord is used to lower vertically a blo...

A cord is used to lower vertically a block of mass `M`, a distance `d` at a constant downward acceleration of `(g)/(4)`, then the work done by the cord on the block is

A

`Mg(d)/(4)`

B

`3Mg(d)/(4)`

C

`-3Mg(d)/(4)`

D

`Mgd`

Text Solution

Verified by Experts

The correct Answer is:
C
When the block moves vertically downward with acceleration `(g)/(4)`, then tension in the cord
`T=M(g-(g)/(4))=(4)/(4)Mg`
Work done by the cord
`=vecFvecs=Fscostheta`
`Tdcos(180^@)=-((3Mg)/(4))xxd=-3Mg(d)/(4)`
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