For the stationary observer:Frequency of the sound produced by the whistle, ν = 400 HzSpeed of sound = 340 m/sVelocity of the wind,v= 10 m/sAs there is no relative motion between the source and the observer, the frequency of the sound heard by the observer will be the same as that produced by the source, i.e., 400 Hz.The wind is blowing toward the observer. Hence, the effective speed of the sound increases by 10 units, i.e.,Effective speed of the sound,ve= 340 + 10 = 350 m/sThe wavelength (λ) of the sound heard by the observer is given by the relation:λ=ve/v= 350/400 = 0.875 m

For the running observer:Velocity of the observer,vo= 10 m/sThe observer is moving toward the source. As a result of the relative motions of the source and the observer, there is a change in frequency (v‘).This is given by the relation:

Since the air is still, the effective speed of sound = 340 + 0 = 340 m/sThe source is at rest. Hence, the wavelength of the sound will not change, i.e.,λremains 0.875 m.Hence, the given two situations are not exactly identical.