SAT Subject Physics Practice Question 39: Answer and Explanation

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Question: 39

5. Two objects, one of mass 3 kg and moving with a speed of 2 m/s and the other of mass 5 kg and speed 2 m/s, move toward each other and collide head-on. If the collision is perfectly inelastic, find the speed of the objects after the collision.

A. 0.25 m/s
B. 0.5 m/s
C. 0.75 m/s
D. 1 m/s
E. 2 m/s

Correct Answer: B


By definition of perfectly inelastic, the objects move off together with one common velocity, v′, after the collision. By conservation of linear momentum,

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