MCAT Physics Question 101: Answer and Explanation

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Test Information

Question: 101

11. A student is measuring sound frequencies from the side of a road while walking east. For which of the following situations could the student determine that the difference between the perceived frequency and the actual emitted frequency is zero?

  • A. A plane flying directly above him from east to west
  • B. A police car passing the student with its siren on
  • C. A person playing piano in a house on the street
  • D. A dog barking in a car that moves east

Correct Answer: D

Explanation:

This question is testing us on our understanding of the Doppler effect. A difference of zero between the perceived and the emitted frequencies implies that the source of the sound is not moving relative to the student. If the car in choice (D) is moving at the same speed as the student, then the relative motion between them could be 0. In all of the other cases, the student and the sound source are necessarily moving relative to each other.

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