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A 400 Hz siren approaches a still observer at one fifth of the speed of sound. What frequency is heard?
A500 Hz
B320 Hz
C480 Hz
D400 Hz
Answer & Solution
Correct answer: A. 500 Hz
Heard frequency is 400 divided by (1 minus 1/5), which is 400 over 0.8, giving 500 Hz.
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