SAT Subject Physics Practice Question 315: Answer and Explanation

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Question: 315

11. A train engine that weighs 5000N stops at the exact center of a bridge. The bridge weighs 75,000N and has two equally spaced pillars that completely support the bridge. The sum of the torques

A. 75,000N
B. 40,000N
C. 37,500N
D. 2500N
E. 0N

Correct Answer: E

Explanation:

The correct answer is (E). The engine stops exactly at the center of the bridge, which means the weight of the train passes through the center of gravity of the bridge. The lever arm is zero, which means there cannot be any torques, because a torque is the product of an applied force and a lever arm.

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