High speed train sounding horn - Doppler effect

AI Thread Summary
To calculate the frequency of the sound perceived by a person at a crossing as a high-speed train moves away, the correct formula is f0 = fs / (1 + vs/v), where fs is the source frequency and vs is the speed of the source. In this case, the train's horn frequency is 416 Hz, and the train's speed is 41 m/s while the speed of sound is 345 m/s. The correct calculation yields an observed frequency of approximately 366.6 Hz. The key point is to use a positive sign in the denominator when the source is moving away from the observer. This adjustment resolves the initial confusion in the calculation.
conniechiwa
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A high speed train is traveling at a speed of 41 m/s when the engineer sounds the 416 Hz warning horn. The speed of sound is 345 m/s. What is the frequency of the sound as perceived by a person standing on at the crossing when the train is leaving?

I used the equation: f0=fs/(1-vs/v)
f0=416 Hz / 1-(41 m/s / 345 m/s)
f0=366.6

I'm not sure what I'm doing wrong... =(
 
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You want to find the observed frequency for when the train is moving away from the observer. When the source is moving away from the observer, the sign in the denominator is positive, not negative. That is you problem.
 
oh okay thanks!
 
No problem. :smile:
 

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