a chain of lenght L is lying on a table with 1/3 of its lenght hanging down. Calculate the work done in pulling the chain up to the surface of table

this question can easily be solved if we consider the motion of center of mass of hanging part....

at intial moment L/3 length was hanging , so the distance of center of mass of this hanging part the from table is L/6...

mass of this hanging part = M/3

finally when the chain is pulled up then center of mass of hanging part is on table ....

workdone = mgdh                        (dh = change in height)

m = M/3 , h = L/6

work = M/3 *g* L/6

      =MGL/18

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Approved