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A person standing close to a railroad crossing hears the whistle of an approaching train. He notes that the pitch of the whistle drops as the train passes by and moves away from the crossing. The frequency of the distant approaching whistle is 546 Hz; it drops to 469 Hz after the train is well past the crossing. What is the speed of the train? Use 340 m/s for the speed of sound in air.

Hint: Calculate the ratio of frequency of the whistle before and after the crossing. That ratio does not include the frequency of the train at rest.

The best I've been able to come up with is:

546 Hz=507.5 Hz (340 m/s/(340 m/s-X))

1.076=(340/(340-X))

1.076(340-X) = 340

365.8 - 1.076X = 340

-1.076X = - 25.8

X=23.97 m/s

Any suggestions?

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# Homework Help: Frequency/Speed of sound

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