For the standing observer:

Frequency is given as

Velocity of sound is given as

Speed of the wind is given as

Because there is no relative motion between the observer and the truck, the observer will hear the horn at ..

The wind blows in the observer’s direction at .

Effective velocity of the sound will be,

The wavelength of the sound can be calculated as

For the observer running towards the train :

Speed of the observer is given as

We know,

The apparent frequency of the sound as the observers move towards the truck is :

=

=

As the air is still the effective velocity of sound is still .

As the truck is stationary the wavelength remains .

Hence, the two cases are not completely identical.