A stationary horn emits a sound with a frequency of 249 Hz A

A stationary horn emits a sound with a frequency of 249 Hz. A car is moving away from the horn on a straight road with constant speed. If the driver of the car hears the horn at a frequency of 221 Hz, then what is the speed of the car? Use 340 m/s for the speed of the sound.

Solution

f = Fo•(V + Vr)/(V+Vs)
f = 221 Hz
Fo = 249 Hz
V = speed of sound = 340 m/s
Vr = velocity of receiver
Vs = velocity of sender = 0

221 = 249 * (340 - Vr) / 340
Vr = 38.2 m/s