AP Physics 1 Question 391: Answer and Explanation

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Question: 391

9. A student drops a 1 kg rock off a cliff with a height of 20 m. The rock lands on the ground and comes to rest in 0.25 seconds. What was the magnitude of the average force that the rock experienced while coming to rest?

  • A. 20 N
  • B. 40 N
  • C. 80 N
  • D. 160 N

Correct Answer: C



The gravitational potential energy of the rock is converted into kinetic energy. This allows you to calculate the final speed of the rock when it lands:

The average force experienced by the rock can be calculated using