Question

A car sounding its horn at 480Hz moves towards a high wall at a speed of 20m/s, the frequency of the reflected sound heard by the man sitting in the car will be nearest to __________

(a) 480Hz

(b) 510Hz

(c) 540Hz

(d) 570Hz

I got this question in a job interview.

I'd like to ask this question from Stationary Waves in division Waves of Engineering Physics I

Answer 1

Correct choice is (c) 540Hz

The best I can explain: After reflection from the wall, the sound moves towards observer in the car,

γ^‘=(v+v0)/(v-vs)×γ=(340+20)/(340-20)×480=540Hz.