Question

A train, standing at the outer signal of a railway station blows a whistle of frequency 400 Hz In still air. 

1. What Is the frequency of the whistle for a platform observer when the train 

(a) approaches the platform with a speed of 10 m s^-1 , 

(b) recedes from the platform with a speed of 10 m s^-1? 

2. What Is the speed of sound in each case? The speed of sound in still air can be taken as 340 m s^-1 .

Answer 1

Given, f = 400 Hz v = 340 ms-1 vs = 10 ms^-1 : speed of train . 

1. (a) train approaches the platform

(b) train recedes from the platform

2. The speed of sound does not change, i.e., it is 340 ms^-1 for both cases.