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A sound source is moving toward a microphone: Pulses, sound frequency

A sound source is moving toward a microphone at 25 m/s, emitting sound at a constant frequency of 740 Hz (i.e. 740 pulses per second). If the source starts out 5 meters from the microphone then:

-how many pulses are emitted as the source approaches the microphone?
-how long is it between the instant the microphone receives the first pulse and the last?
-what sound frequency is therefore received by the microphone?

Assume sound travels at 340 m/s.

Solution Preview

5/25=0.2 (s)........time required for pulses to arrive at the microphone
N=740*0.2=148 ...

Solution Summary

With explanations and calculations, the problems are solved.