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

Answer: velocity of the car is 113.33m/s

Explanation:

From Doppler effect,

in the case which the source is moving towards the observer at rest

f2 = v / (v-vs) * f1

where f2 is the final observed frequency

f1 is the initial observed frequency

v = 340m/s (speed of sound in air)

vs = velocity of the source of sound.

rearranging the above equation

f2 * (v - vs) = f1 * v

vs = (f1 * v/f2) - v

but f1 = 80Hz

f2 = 60Hz

v = 340m/s

substituting,

vs = (80 x 340) / 60 - 340

vs = 453.33 - 340

vs = 113.33m/s

velocity of the car is 113.33m/s