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Two blocks of masses $m_1$ and $m_2$ are connected by a massless spring and placed on a smooth surface. The spring is initially stretched and then released. Which of the following statements is/are correct? A. The momentum of each particle remains constant separately. B. The momenta of both bodies are equal. C. The magnitudes of the momenta of both bodies are equal to each other. D. The mechanical energy of the system remains constant.

1. A, B and C are correct
2. A, B and D are correct
3. C and D are correct
4. Only C is correct

Correct answer: C and D are correct

Solution

Since the surface is smooth, there is no external horizontal force on the system, so total momentum is conserved. The spring exerts equal and opposite internal forces, so the blocks acquire equal and opposite momenta in magnitude, not separately constant momenta. Because the spring is ideal and the surface is smooth, mechanical energy remains constant.

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