A cord is used to lower vertically a block of mass M by a distance d with constant downward accelera

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5.Work, Energy, Power and Collision

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A cord is used to lower vertically a block of mass $M$ by a distance $d$ with constant downward acceleration $\frac{g}{4}$. Work done by the cord on the block is

A

$mg\frac{d}{4}$

B

$3mg\frac{d}{4}$

C

$-3mg\frac{d}{4}$

D

$Mgd$

Solution

The equation of motion $\mathrm{Mg}-\mathrm{R}=\mathrm{Ma}$

$\mathrm{R}=\mathrm{M}(\mathrm{g}-\mathrm{a})=\mathrm{M}\left(\mathrm{g}-\frac{\mathrm{g}}{4}\right)=\frac{3 \mathrm{Mg}}{4}$

Work done by the cord $=-\mathrm{Rd}$

$=-\frac{3}{4} \mathrm{Mgd}$

Standard 11

Physics

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