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? The speed of sound in the air is 343 m/s.
A) 64.0 m/s
B) 49.0 m/s
C) 16.0 m/s
D) 36.0 m/s
E) 25.0 m/s

Question

Quizplus · Accepted Answer

We can use the Doppler effect formula to solve this problem:
f₂ = f₁(v±v₀) / (v∓vs)
where f₁ is the frequency of the horn as heard by the observer (80 Hz), f₂ is the frequency of the horn as heard after passing the observer (60 Hz), v is the speed of sound (343 m/s), v₀ is the speed of the observer (0 m/s), and vs is the speed of the source (the car). 
Plugging in the values, we get:
60 = 80(v-v_s) / (v+343)
Simplifying and solving for v_s, we get:
v_s = 49.0 m/s
Therefore, the answer is (B) 49.0 m/s.

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