A railroad train is traveling at a speed of 26.0 m/s in still air. The frequency
ID: 1477626 • Letter: A
Question
A railroad train is traveling at a speed of 26.0 m/s in still air. The frequency of the note emitted by the locomotive whistle is 380 Hz.Use 344 m/s for the speed of sound in air.
A)What is the wavelength of the sound waves in front of the locomotive? m
B)What is the wavelength of the sound waves behind the locomotive? m
C)What is the frequency of the sound heard by a stationary listener in front of the locomotive? Hz
D)What is the frequency of the sound heard by a stationary listener behind the locomotive? Hz
Explanation / Answer
Given: speed of source VS = 26.0 m/s
freq. of sound wave f = 380 Hz
speed of sound wave V = 344 m/s
A) .................
in front, at a cnst. point on the train or the point on the platform ????
where?
if it is a cnst. point on the whistle,
wavelength = V / f
= 344 /380
=0.9 m
B) ................
if it is a constant point on a platform behind the train,
as same as ....(D)
C) freq. Observed f ' = f [ V / ( V - VS) ]
=380* [344 / (344-26.0)]
=380* [344 / 318 ]
= 411.1 Hz
D) freq. Observed f ' = f [ V / ( V + Vs ) ]
= 380* [344 / (344+26.0)]
= 380 * [ 344 / 370 ]
= 380 * 0.9297
= 353.2973 Hz
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