A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in air is 343 m/s.
A) 68 Hz
B) 69 Hz
C) 70 Hz
D) 71 Hz
E) 72 Hz

Question

Quizplus · Accepted Answer

The Doppler effect formula for a source moving towards and then away from an observer can be used. When the car approaches, the observed frequency is higher, and when it moves away, it is lower. Solving the equations for both scenarios gives the emitted frequency as 70 Hz.

A Car Approaches You at a Constant Speed, Sounding Its