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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?

Asked in AIEEE 2004 · Work done by gravity and contact forces

• (1) 7.2 J
• (2) 3.6 J
• (3) 120 J
• (4) 1200 J

Step-by-step solution

Why the other options are wrong

• (1) Comes from raising the hanging mass through the full 0.6 m instead of its centre-of-mass height 0.3 m.
• (3) No single slip gives 120 J. Sanity check: raising 1.2 kg through 0.3 m cannot need more than a few joules.
• (4) No single slip gives 1200 J. Sanity check: it would lift the whole 4 kg chain through 30 m.

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