Question

A uniform chain of length $2 \,m$ is kept on a table such that a length of $60 \,cm$ hanges freely from the edge of the table. The total mass of the chain is $4 \,kg$. The work done in pulling the entire chain on the table (Take $g = 10 \,ms^{-2}$)

• A. $12.9\, J$
• B. $6.3\, J$
• C. $3.6\, J$
• D. $2.0\, J$

Answer 1

Answer: (C)

Mass of length $2 \,m$ of the chain $= 4\, kg$
Mass of length $60\, cm$ or $0.60\, m$ of the chain
$ = \frac{4 \times 0.60}{2} = 1.2\,kg$
Weight of the hanging part of the chain
$= 1.2 \times 10 = 12 \,N$
Since the centre of gravity of the hanging part lies at its mid point, i.e. $30\, cm$ or $0.30 \,m$
$\therefore W = 12 \times 0.30 = 3.6\,J$