Doppler Effect

Two trucks heading in opposite directions with speeds of $60 \mathrm{kmph}$  and $70 \mathrm{kmph}$ respectively, approach each other. The driver of the first truck sounds his horn of frequency  $400 \mathrm{Hz}$. What frequency does the driver of the second truck hear? (velocity of sound $330 \mathrm{m}/\mathrm{s}$) After the two trucks have passed each other, 

A train sounds its whistle as it approaches and crosses a level crossing. An observer at the crossing measures a frequency of $219 \mathrm{Hz}$ as the train approaches and a frequency of $184 \mathrm{Hz}$ as it leaves. If the speed of sound is taken to be $340 \mathrm{m}/\mathrm{s}$, find the speed of the train and the frequency of its whistle.
 

What is Doppler shift? Obtain an expression for the apparent frequency of sound heard when the observer is in motion with respect to a source at rest.

What is Doppler effect? Obtain an expression for the apparent frequency of sound heard when the source in  motion with respect to an observer at rest.

What is 'Doppler effect ? Give illustrated example.

Write down an expression for the observed frequency when both source and observer are moving relative to each other in the same direction.

What is Doppler effect? Give an example.

A train, standing in a station-yard, blows a whistle of frequency $400Hz$ in still air. The wind starts blowing in the direction from the yard to the station with at a speed of $10m{s}^{-1}$. What are the frequency, wavelength, and speed of sound for an observer standing on the station’s platform? Is the situation exactly identical to the case when the air is still and the observer runs towards the yard at a speed of $10m{s}^{-1}$? The speed of sound in still air can be taken as $340m{s}^{-1}.$