AP Physics 1 Question 57: Answer and Explanation

Test Information

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Question: 57

7. A person standing on a horizontal floor is acted upon by two forces: the downward pull of gravity and the upward normal force of the floor. These two forces

  • A. have equal magnitudes and form an action-reaction pair
  • B. have equal magnitudes and do not form an action-reaction pair
  • C. have unequal magnitudes and form an action-reaction pair
  • D. have unequal magnitudes and do not form an action-reaction pair

Correct Answer: B

Explanation:

B Because the floor is horizontal the weight and normal force balance each other out, so these two forces do have equal magnitudes (eliminate (C) and (D)). These two forces, however, do not form an action-reaction pair. In order to form an action-reaction pair two forces must be acting on each other. The correct action-reaction pair in this situation is Earth's pull on the person, weight, and the person's pull on Earth.