SAT Subject Physics Practice Question 369: Answer and Explanation

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Question: 369

65. A stuntman drives a brand new 800kg sports car off a high cliff at 200 km/hour. At the exact moment that the car is driven off the cliff, an 800kg rock is dislodged and falls straight down toward the ground. Which of the following is a correct statement about the event?

A. The car hits the ground first.
B. The rock hits the ground first.
C. The car and the rock hit the ground at the same time.
D. The x velocities of the car and the rock equalize over a period of time.
E. The x accelerations of the car and the rock are different

Correct Answer: C

Explanation:

The correct answer is (C). All objects in free fall near the earth are accelerated toward the earth at the same rate. Even though the car is moving along the x-axis at a high rate of speed, as soon as it clears the edge of the cliff it is in free fall. Both the rock and the car start with a y velocity of zero and reach the ground at the same time.

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