Question

A uniform chain of length L and mass M is lying on a smooth table and one third of its length is hanging vertically down over the edge of the table. If g is acceleration due to gravity, the work required to pull the hanging part on to the table is

• A. $M g L$
• B. $\frac { M g L } { 3 }$
• C. $\frac { M g L } { 9 }$
• D. $\frac { M g L } { 18 }$

Answer 1

Answer: (D)

$\frac { M g L } { 18 }$

Answer 2

As 1/3 part of the chain is hanging from the edge of the table. So by substituting n = 3 in standard expression

$= \frac { M g L } { 2 ( 3 ) ^ { 2 } } = \frac { M g L } { 18 }$.