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smsport
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Homework Statement
A car and a bicycle are traveling directly toward each other at different speeds. The car horn has a frequency of 440Hz, and the car is traveling at 15.0m/s. The cyclist hears a sound of frequency 467Hz. The velocity of sound in air is 343m/s.
i) Calculate the frequency of the signal emitted into the air by the moving car along the straight line joining the car to the bicycle.
ii) Calculate the speed of the bicycle.
iii) What frequency would the cyclist hear if the car and the bicycle were moving directly away from each other with the same speeds with which they were approaching each other in the previous part?
Homework Equations
For observer and source both moving:
fobserver=fsource [(1+ or - vobserver/v)/(1+ or -vsource/v)]
v= velocity of sound in air
signs in numerator: + if observer moving toward source and - if away from source
signs in denominator: - if source moving toward observer and + if away from observer
The Attempt at a Solution
For question i) it does not appear that I need to calculate anything. If the car horn has a frequency of 440 Hz then this is the frequency of the signal emitted into the air. If I am grossly missing something here please advise. It seems it is jusk asking for freq of the signal emitted into the air so for anything that would be whatever the frequency of the source is, right? Therefore, 440 Hz.
ii) Using the equation above for source and observer moving toward each other:
467=440[(1+vo/343)/1-15.0/343)]
Solve for vo to get the speed of the bicycle: 4.5m/s
iii) Using the equation above for source and observer moving away from each other:
fobserver=440[(1-4.5/343)/1+15.0/343)] = 416 Hz
Now this all seems pretty straightforward except that question i threw me off. Obviously, if I'm incorrect about my assumptions about frequency of the sound emitted into the air then the rest of my answers will also be wrong. If I am wrong, please help explain what fundamental concept about frequency I'm missing and how to then calculate the frequency of a sound emitted into air. Thanks!
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