Question

A car is moving at a rate of 50 m/s when suddenly the driver hit the horn that

emits 20000Hz frequency. What will be the perceived frequency of a man

standing at the sidewalk if the speed of the sound is 340 m/s and the car is

moving away from the location of the man?

Answer 1

We can find the frequency observed by the man from the Doppler Shift formula:

$$f_o=f_s(\dfrac{v}{v+v_s}),$$ $$f_o=2\times10^4\ Hz\times(\dfrac{340\ \dfrac{m}{s}}{340\ \dfrac{m}{s}+50\ \dfrac{m}{s}})=1.74\times10^4\ Hz.$$