A stationary source emits a sound wave of frequency f. If it were possible for a man to travel toward the source at the speed of sound, he would observe the emitted sound to have a frequency of:
A) zero
B) f/2
C) 2f/3
D) 2f
E) infinity

Question

Quizplus · Accepted Answer

This is an example of the Doppler effect. When a source emitting waves is moving toward an observer, the observer will receive waves with a higher frequency than the emitted frequency. The formula for the Doppler effect is given by (v is velocity of the observer, c is velocity of wave, and f is frequency): f' = f(c+v)/c. When the observer is traveling at the speed of sound, v = c. Therefore, f' = f(2c)/c = 2f.

A Stationary Source Emits a Sound Wave of Frequency F