SAT Subject Physics Practice Question 40: Answer and Explanation

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Question: 40

6. Object #1 moves toward object #2, whose mass is twice that of object #1 and which is initially at rest. After their impact, the objects lock together and move with what fraction of object #1’s initial kinetic energy?

A.
B.
C.
D.
E. None of the above

Correct Answer: D

Explanation:

First, apply conservation of linear momentum to calculate the speed of the combined object after the (perfectly inelastic) collision.

Therefore, the ratio of the kinetic energy after the collision to the kinetic energy before the collision is

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