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 the 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 frequency heard when the source is approaching is f' = f(v + vo)/(v - vs) and when receding is f' = f(v - vo)/(v + vs). Solving these equations simultaneously with given frequencies (76 Hz and 65 Hz) and speed of sound (343 m/s) gives the emitted frequency as 70 Hz.

A Car Approaches You at a Constant Speed,sounding Its Horn,and