Q. A uniform chain of length 2 m is kept on a table such that a length of 60 cm hangs freely from the edge of the table. The total mass of the chain is 4 kg. What is the work done in pulling the entire chain on the table?
A) 7.2 J
B) 3.6 J
C) 120 J
D) 1200 J
Explanation
(b) Mass per unit length=$\frac{M}{L}$
$= \frac{4}{2} = 2kgm^{- 1}$
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The mass of 0.6 m of chain
$\ = 0.6 \times 2 = 1.2kg$
$\therefore$Center of mass of hanging part
$h = \frac{0.6 + 0}{2} = 0.3m$
Hence, work done in pulling the chain on the table =work done against gravity force
$W = mgh = 1.2 \times 10 \times 0.3 = 3.6\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.