PHY 122
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I have a question pertaining to problem number 20 in set 56 for the part how many pulses received were emitted before the microphone was within 40 meters of the source. here are we assuming that the microphone did not move past 40 meters even though it had to move X distance before it reached the source that was emitted in the opposite direction?
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I do not understand how to calculate the number of pulses received were emitted before the microphone was within 40 meters of the source when it started out at a distance 40 meters from the source?
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The first pulse was received when the detector was 40 m away from the source. So it must have been emitted before the detector, which is traveling toward the source, reached the 40 m position. Specifically it was emitted earlier by the time equal for the pulse to travel the 40 m distance.
We could have figured out where the detector was at that instant, assuming had been traveling long enough, and could have then figured out how many pulses there were in the intervening distance. However we chose a different approach, based on time intervals. Both approaches would yield the same solution.