SAT Subject Physics Practice Question 374: Answer and Explanation

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Question: 374

70. A 30N child can push open a 1000N door because

A. the torque the child exerts on the door is greater than the torque the door exerts on the child.
B. the lever arm through which the child's force is exerted is less than the lever arm through which the door's weight is exerted.
C. the door's center of gravity is located at the bottom hinge.
D. the door's center of gravity is located at the top hinge.
E. the door's center of gravity is located at the doorknob.

Correct Answer: A

Explanation:

The correct answer is (A). An unbalanced torque causes motion to occur. The child can push the door open because she applies the unbalanced torque.

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