Posted by **sophie** on Saturday, April 4, 2009 at 8:00pm.

A car moving at 16.0 m/s, passes an observer while its horn is pressed. Find the difference between the frequencies of sound heard when the car approaches and when it recedes from the stationary observer. The velocity of sound is 343 m/s and the frequency of the sound of the car's horn is 583 Hz.

A. 42.2 Hz

B. 54.5 Hz

C. 61.8 Hz

D. 65.4 Hz

I used the Dopler effect formula and got B?

- Physics!! -
**drwls**, Saturday, April 4, 2009 at 8:13pm
The shift in frequency is, for slow speeds compared to the speed of sound, f*(V/a) = 583*(16/343) = 27.2 Hz , up or down. a is the speed of sound

Double that for the difference between the upshifted and the downshifted frequencies and you get 54.4 Hz

The correct answer is B. Good work.

The exact equation, which I am too lazy to look up, would probably give you 54.5 Hz

- Physics!! -
**sophie**, Saturday, April 4, 2009 at 8:19pm
thanks!

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