AP Physics 1 Question 345: Answer and Explanation

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Question: 345

3. Which of the following concerning uniform circular motion is true?

  • A. The centrifugal force is the action/reaction pair of the centripetal force.
  • B. The centripetal acceleration and velocity point in the same direction.
  • C. The velocity of the object in motion changes, whereas the acceleration of the object is constant.
  • D. A satellite undergoing uniform circular motion is falling toward the center even though its path is circular.

Correct Answer: D



The centripetal force is a name given to the net force of an object undergoing uniform circular motion. Therefore, it is not a separate force and does not have an action/reaction pair. This eliminates (A). Since the speed is constant but direction changes, acceleration must be perpendicular to velocity; eliminate (B). Not only does velocity change with time, but the acceleration also changes because the direction of the centripetal acceleration always points to the center of the circle. This eliminates (C). A satellite undergoing uniform circular motion is in fact falling (accelerating due to gravity) toward the center, but doesn't get closer due to its tangential velocity. Its velocity is always tangent to its circular path.