Question

A policeman blows a whistle with a frequency of 500hz. A car approaches him with a velocity of 15m/s.Calculate the change in frequency as heard by the driver of the car before and after crossing the policeman .Speed of sound in air is 300m/s.

Answer 1

A policeman blows a whistle of frequency 300Hz as a car speeds past him with a velocity of 18 km/hr .find the change in frequency as heard by the driver of the car just as he passes the policeman. Velocity of sound is 340m/s

Here the change in frequency can be calculated in accordance with the Doppler Effect.

So the answer for your question is 50 Hz.