A man driving a car toward a large vertical wal sounds his horn. The car is traveling at 81 km/h. The echo off the wall is heard by the man at a frequency of 958 Hz. What is the frequency of the car's horn?

Question

A man driving a car toward a large vertical wal sounds his horn.  The car is traveling at 81 km/h.  The echo off the wall is heard by the man at a frequency of 958 Hz.  What is the frequency of the car's horn?

Henry · Answer

Vc = 81000m/3600s = 22.5 m/s. = Velocity of car. F = ((V+Vr)/(V+Vc)))*Fh = 958Hz. ((345+22.5)/(343-22.5))*Fh = 958 367.5Fh/322.5 = 958 1.140Fh = 958 Fh = 841 Hz. = Freq. of horn.