AP Physics 1 Question 11: Answer and Explanation

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Question: 11

1. A horizontal spring-block oscillator is in motion when a second block of equal mass falls on top of the oscillating block. If the two blocks stick together, what effect will this have on the amplitude of the oscillations?

  • A. It will increase the amplitude.
  • B. It will decrease the amplitude.
  • C. It will have no effect.
  • D. It would depend on where the original block was in its cycle when the second block fell.

Correct Answer: D


D Conservation of Linear Momentum tells us that the speed will always be reduced if the original block is in motion. Though the added mass will somewhat compensate for this effect, the kinetic energy will still be reduced. Therefore, the overall energy of the system will go down, which will reduce the amplitude of oscillation. However, it is only kinetic energy that will be reduced when the block is added, so there will be no effect if it comes when the system possesses only potential energy (at maximum displacement from equilibrium).