(a)Frequency of the whistle, ν = 400 Hz
Speed of the train, vT= 10 m/s
Speed of sound, v = 340 m/s
The apparent frequency (V') of the whistle as the train approaches the platform is given by the relation:
The apparent frequency (V'') of the whistle as the train recedes from the platform is given by the relation:
The apparent change in the frequency of sound is caused by the relative motions of the source and the observer. These relative motions produce no effect on the speed of sound.
Therefore, the speed of sound in air in both the cases remains the same, i.e., 340 m/s.