Question

A person is standing on a railway platform and a train is approaching to him, what is maximum wavelength of sound he can hear? Wavelength of whistle=1m, speed of sound in air=330m/s, speed of train=36km/h.

(a) 1m

(b) 32/322m

(c) 33/32m

(d) 12/13m

This question was addressed to me during an interview.

The above asked question is from Stationary Waves topic in chapter Waves of Engineering Physics I

Answer 1

The correct answer is (b) 32/322m

For explanation: As γ^‘=v/(v-vs)×γ

vs=36km/h=10m/s

ʎ^‘=(v-vs)/v×ʎ=(330-10)/330×1=32/33 m.