SAT Subject Physics Practice Question 117: Answer and Explanation

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Question: 117

12. A car is traveling at 20 m/s away from a stationary observer. If the car’s horn emits a frequency of 600 Hz, what frequency will the observer hear? (Use v = 340 m/s for the speed of sound.)

A. (34/36)(600 Hz)
B. (34/32)(600 Hz)
C. (36/34)(600 Hz)
D. (32/34)(600 Hz)
E. (32/36)(600 Hz)

Correct Answer: A


Since the car is traveling away from the stationary detector, the observed frequency will be lower than the source frequency. This eliminates B and C. Using the Doppler effect equation, we find that

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