SAT Subject Physics Practice Question 398: Answer and Explanation

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Question: 398

4. A 12,500 kg boxcar rolling through a freight yard has a velocity of 1 m/s when it strikes another boxcar of the same mass that is at rest. Both cars stick together and continue to roll down the track with a momentum of

A. 0 kg·m/s
B. 3125 kg· m/s
C. 6250 kg·m/s
D. 12,500 kg·m/s
E. 25,000 kg·m/s

Correct Answer: D


The correct answer is (D). This is a conservation of momentum question. Since the momentum before an event must equal the momentum after an event, the momentum must be 12,500 kg·m/s.

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