Question

The engine of a train moving with speed 10ms^-1 towards a platform sounds a whistle at frequency 400Hz. The frequency heard by a passenger inside the train is (neglect air speed. Speed of sound in air 330ms^-1) 

(1) 200Hz 

(2) 400Hz 

(3) 412 Hz 

(4) 388 Hz

Answer 1

Correct option is (2) 400Hz 

The relative velocity of a passenger with source of sound (engine) is 0. So there will be no doppler’s effect. So frequency heard is 400 Hz.