SAT Subject Physics Practice Question 664: Answer and Explanation
15. A mass is suspended by a rubber band. The rubber band is stretched by the weight of the mass, but it is not moving. The action force that causes the rubber band to stretch comes from the earth. What is the reaction force of the force pair?
A. The rubber band pulling on the mass
B. The rubber band pulling on the earth
C. The mass pulling on the rubber band
D. The mass pulling on the earth
E. The earth pulling on the rubber band
Correct Answer: D
The correct answer is (D). According to Newton's Third Law, the action-reaction force pair must be equal in magnitude and oppositely directed. The earth pulls on the mass, and the mass pulls on the earth (the pair) with the same force.