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# A cord is used to lower vertically a block of mass M,a distance d, at a constant downward acceleration $g/4$. Then work done by cord on block

$(a)\;\frac{-3Mgd}{4} \quad (b)\;\frac{Mgd}{4} \quad (c)\; \frac{3Mgd}{4} \quad (d)\;Mgd$

Let T be tension in the string
$Mg-T=\large\frac{Mg}{4}$
$T=Mg-\large\frac{Mg}{4}$
$\quad=\large\frac{3 Mg}{4}$
Work done by tension
$\quad=-T \times d$
$\quad =\large\frac{-3Mg}{4}$$\times d$
$\quad=\large\frac{-3Mgd}{4}$
Hence a is the correct answer
edited Jun 11, 2014

+1 vote