SAT Subject Physics Practice Question 598: Answer and Explanation

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Question: 598

9. An object at rest is placed into free fall at a height of 20 m. What is the velocity of the object when the PE equals the KE?

A. 8 m/s
B. 11 m/s
C. 14 m/s
D. 17 m/s
E. Velocity cannot be determined.

Correct Answer: C


The correct answer is (C). The problem may be solved in several ways. Perhaps the best solution is a little thought. The potential energy and the kinetic energy are equal to one another when the object has fallen half the distance to the ground, or 10 m. All we have to do now is treat the problem as a free fall problem by restating the situation a little. The velocity of an object that starts from rest and free falls 10 m? The solution is found by .

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