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A boy of mass 50 kg sprints at 10 m/s and leaps onto a stationary cart resting on a frictionless floor. After he lands, the cart together with the boy moves at 2.50 m/s. Determine the mass of the cart.

1. 150 kg
2. 100 kg
3. 200 kg
4. 120 kg

Correct answer: 150 kg

Solution

Conservation of momentum gives m_boy*u = (m_boy + m_cart)*v, from which the cart mass is 150 kg.

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