As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 80.0 Hz. After the car goes by, you hear a frequency of 60.0 Hz. What is the speed of the car? Assume that he speed of sound in air is 343 m/s.
A)64 m/s
B)49 m/s
C)16 m/s
D)36 m/s
E)25 m/s

Question

Quizplus · Accepted Answer

Using the Doppler effect formula for sound, the observed frequency when the source approaches is higher, and when it moves away, it is lower. Solving the equations for the given frequencies and speed of sound gives the speed of the car as 49 m/s.

As You Stand by the Side of the Road, a Car