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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- May 20th 2008, 01:44 PMcheckmarksdoppler 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?

- May 20th 2008, 01:54 PMCaptainBlack
If the range rate of the car is $\displaystyle v$, then the recieved frequency will be $\displaystyle f_0 (1-2v/c) $, where $\displaystyle c$ is the speed of sound and $\displaystyle f_0$ is the source frequency, the $\displaystyle 2$ is because this is a two way doppler.

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

RonL