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