An automobile traveling at 45 mi/h (= 20.0 m/s)blows a horn at a constant 600 Hz.What is the frequency observed by a stationary observer as the car approaches?
A)512 Hz
B)567 Hz
C)600 Hz
D)612 Hz
E)638 Hz

Question

Quizplus · Accepted Answer

The observed frequency is higher due to the Doppler effect. The formula for the observed frequency is f' = f * (v + vo) / (v - vs), where f is the source frequency, v is the speed of sound in air (~343 m/s), vo is the observer's speed (0 m/s), and vs is the source speed (20 m/s). Plugging in the values gives approximately 638 Hz.

An Automobile Traveling at 45 Mi/h (= 20