SAT Subject Physics Practice Question 245: Answer and Explanation

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Question: 245

16.

If the rod is uniform and has mass m, what is the tension in the supporting string?

A.
B.
C.
D.
E. mg

Correct Answer: D

Explanation:

With respect to the point at which the rod is attached to the vertical wall, the tension in the string exerts a counterclockwise (CCW) torque, and the gravitational force—which acts at the rod’s center of mass—exerts a clockwise (CW) torque. If the rod is in equilibrium, these torques must balance. Letting L denote the length of the rod, this gives us

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