SAT Subject Physics Practice Question 242: Answer and Explanation

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Question: 242

13. Two people, one of mass 100 kg and the other of mass 50 kg, stand facing each other on an ice-covered (essentially frictionless) pond. If the heavier person pushes on the lighter one with a force F, then

A. the force felt by the heavier person is –F
B. the force felt by the heavier person is –2F
C. the magnitude of the acceleration of the lighter person will be of the magnitude of the acceleration of the heavier person
D. the magnitude of the acceleration of the lighter person will be twice the magnitude of the acceleration of the heavier person
E. None of the above

Correct Answer: D

Explanation:

By Newton’s third law, the force on the heavier person is equal but opposite to the force on the lighter person, eliminating A and B. Since the lighter person has the mass of the heavier person and acceleration is inversely proportional to mass, the magnitude of the lighter person’s acceleration will be twice that of the heavier person.

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