MCAT Physics Question 95: Answer and Explanation
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Question: 95
5. The period for a certain wave is 34 ms. If there is a Doppler shift that doubles the perceived frequency, which of the following must be true?
I. The detector is moving toward the source at a velocity equal to the speed of sound.
II. The source is moving toward the detector at a velocity equal to half the speed of sound.
III. The perceived period is 17 ms.
IV. The perceived period is 68 ms.
- A. III only
- B. I and IV only
- C. II and III only
- D. I, II, and IV only
Correct Answer: A
Explanation:
Period is inversely related to frequency. Because the perceived frequency is doubled, the perceived period must be halved, from 34 ms to 17 ms. While either condition I or II would cause a doubling of the perceived velocity, neither condition must necessarily be true because the opposite could be true instead.