Question

A stationary source is emitting sound at a fixed frequency f₀ , which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is 1.2% of f₀ . What is the difference in the speed of the cars (in km per hour) to the nearest? The cars are moving at constant speeds much smaller than the speed of sound which is 330ms^-1. 

Answer 1

Firstly, car will be treated as an observer which is approaching the source. Then, it will be treated as a source, which is moving in the direction of sound.