A man places a chain (of mass `m` and length `l`) on a table slowly. Initially, the lower end of the chain just touches the table. The man brings down the chain by length `l//2`. Work done by the man in this process is

Options

A. (a) `-mg1/2`
B. (b) `-(mgl)/(4)`
C. (c) `(-3mgl)/(8)`
D. (d) `-(mgl)/(8)`

Answer

C

Explanation

The work done by the man is negative of the magnitude of decrease in potential energy of the chain.
`DeltaU=mgl/2-m/2gl/4=3mgl/g`
`W=--(3mgl)/(8)`