Question

If a train is moving away from an observer, what kind of sound

will the observer hear from the train whistle?
a
It will appear to be lower in pitch than the actual
train whistle
b
It will appear to be higher in pitch than the actual
train whistle
c It will sound the same as the actual train whistle
d It will sound louder than the actual train whistle
e None of the above

Answer 1

a. It will appear to be lower in pitch

Step-by-step explanation:

You want to know what kind of sound an observer will hear from the train whistle if the train is moving away from the observer.

Wavelength

If the train is moving away from the observer, it will be farther from the observer at the end of one cycle of the sound pressure wave than it was at the beginning. Hence the wavelength of the pressure wave will be longer than if the train were stationary. Sounds with longer wavelengths are lower in pitch.

If the train is moving away, the observer will hear a lower pitch whistle.