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Mr. Verma (50 kg) and Mr. Mathur (60 kg) sit at opposite ends of a 4 m long boat (40 kg) that is at rest in water. They both walk to the centre of the boat to discuss a problem. Ignoring water friction, by how much does the boat shift in the water?

1. 40/3 cm
2. 50/3 cm
3. 110/3 cm
4. 10 cm

Correct answer: 40/3 cm

Solution

With CM fixed, m1*d1 + m2*d2 + M*d_boat = 0 where the men's displacements relative to ground are (2 - x) toward centre etc.; solving gives the boat shifts 40/3 cm toward Verma's original side.

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