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

Step-by-step solution

The formula to calculate the frequency of the sound as heard by the passenger inside the train can be written as f ' = f 0 v - v O v - v s       . . . 1 Since the passenger is inside the train, the speeds of the source and the observer are the same. Substitute the values of the known parameters into equation (1) to get the required frequency. f ' = 400 330 - 10 330 - 10   Hz = 400   Hz