SAT Subject Physics Practice Question 16: Answer and Explanation

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Question: 16

7. If all of the forces acting on an object balance so that the net force is zero, then

A. the object must be at rest
B. the object’s speed will decrease
C. the object will follow a parabolic trajectory
D. the object’s direction of motion can change, but its speed cannot
E. None of the above

Correct Answer: E


If Fnet = 0, then a = 0. No acceleration means constant speed (possibly, but not necessarily, zero) with no change in direction. Therefore, B, C, and D are false, and A is not necessarily true.

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