SAT Subject Physics Practice Question 402: Answer and Explanation

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Question: 402

8. The driver of an automobile traveling at 80 km/hr locks his brakes and skids to a stop in order to avoid hitting a deer in the road. If the driver had been traveling at 40 km/hr, how much faster would he have stopped?

A. 4 times the distance
B. 2 times the distance
C. 1/2 the distance
D. 1/4 the distance
E. Not enough information to tell

Correct Answer: D


The correct answer is (D). The same car traveling at twice the velocity has four times the energy. Constant frictional force from the tires will therefore require four times the stopping distance. The car moving at the lower rate only requires 1/4 the stopping distance.

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