Question

A stationary police car emits a sound of frequency 1205 Hz that bounces off of a car on the highway and returns with a frequency of 1255Hz. The police car is right next to the highway, so the moving car is traveling directly toward or away from it.

1. How fast was the moving car going?
2. Was the car moving away or towards the police?
3. What frequency would the police car have received if it had been traveling toward the other car at 25.0m/s?

Answer 1

Let's take the frequency receive by police officer to be

f¹/f²= u-v/u+v

So 1255/1205= 340-v/340+v

V= 6.9m/s positive value implies that the car is moving toward the police

2 to find frequency we use

f/1205= 340+25/340-25

f= 1396Hz