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Math Help - doppler effect and sound waves

  1. #1
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    doppler effect and sound waves

    A sound wave of frequency 300Hz is emitted towards an appproaching car. The wave is reflected from the car and then received back at the emitter at a frequency of 315 Hz. If the speed of sound is 240 m/s, what is the velocity of the car?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by checkmarks View Post
    A sound wave of frequency 300Hz is emitted towards an appproaching car. The wave is reflected from the car and then received back at the emitter at a frequency of 315 Hz. If the speed of sound is 240 m/s, what is the velocity of the car?
    If the range rate of the car is v, then the recieved frequency will be f_0 (1-2v/c) , where c is the speed of sound and f_0 is the source frequency, the 2 is because this is a two way doppler.

    Now an approaching car has negative range rate, so v=-v_{car} , where v_{car} is the car speed.

    RonL
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