Question

The frequency of echo will be ___ Hz if the train blowing a whistle of frequency 320 Hz is moving with a velocity of 36 km/h towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 m/s.

Answer 1

Correct answer is 340

The hill will be a secondary source.

f₁ = frequency of the car w.r.t. the hill

f₂ = Frequency of the sound reflected by hill w.r.t. the car (echo)