Question

Two trains are traveling toward each other. One train is traveling at 31 [m/sec] from our left to the right. The other train is traveling at 40 [m/sec] from the right to the left. The train on the left blows the whistle at fο = 520 [Hz]. a) What is the frequency heard on the other train in still air? b) What is the frequency heard on the other train if there is wind blowing from the right to the left at 20 [m/sec]? c) What the frequency heard if the wind direction were reversed at also 20 [m/sec]?

Answer 1

a) in still air

frequency heard by the right train is f' = (V+Vo)*fo/(V-Vs)

V is the speed of sound in air = 343 m/sec

Vo = 40 m/sec

Vs = 31 m/sec

fo = 520 Hz

f' = (343+40)*520/(343-31) = 638.34 Hz

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b) when the wind is blowing from the right to left is Vw = 20 m/sec

then Now f' = (V+Vw+Vo)*fo/(V+Vw-Vs) = (343+20+40)*520/(343+20-31) = 631.2 Hz

c) in this case

f' = (V-Vw+Vo)*fo/(V-Vw-Vs) = (343-20+40)*520/(343-20-31) = 646.43 Hz