A uniform chain of mass m and length l overhangs a table with its two third part on the table. Find the work to be done by a person to put the hanging part back on the table.

Mass of the part of chain on the table = 2m/3

Mass of the part hanging from the table = m - 2m/3 = m/3


Similarly, length of the part of chain on the table = 2l/3


Length of the part of chain hanging from the table = l/3


Centre of the mass m/3 will be at l/6


Potential energy of the part hanging =


= mgl/18


Work done to put the hanging part back on table = mgl/18


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