A car sounds its horn (502 Hz) as it approachs a pedestrian by the side of the road. The pedestrian has perfect pitch and determines that the sound from the horn has a frequency of 520 Hz. If the speed of sound that day was 340 m/s , how fast was the car travelling

Answer 1

f(observed) = 520 Hz, f(source) = 502 Hz, u = 340 m/s
At source approaching
f(observed) = [v/(v-u)] •f(source),
v =[f(obs)-f(sour)] •u/ f(obs) =
= (520-502) •340/520 = 18•340/520 =
=11.77 m/s.