A person observes two moving trains, A reaching the station and B leaving the station with equal speed of 30 m s - 1 . If both trains emit sounds with frequency 300 Hz , (Speed of sound : 330 m s - 1 ) approximate difference of frequencies heard by the person will be :

Step-by-step solution

Using Doppler effect, apparent frequency is given by f = v ± v 0 v ∓ v s f 0 , where f 0 = actual frequency ,   v 0 = velocity of observer and   v s = velocity of source For train B leaving the station, f 1 = 300 330 - 0 330 - - 30 = 275   Hz ∵ v 0 = 0 For train A reaching the station, f 2 = 300 330 - 0 330 - 30 = 330   Hz The difference of frequencies heard by the person ∆ f = 330 - 275 = 55   Hz