Question

Suppose that a police car on the highway is moving to the right at 20 m/s, while a speeder is coming up from almost directly behind at a speed of 31 m/s, both speeds being with respect to the ground. The police officer aims a radar gun at the speeder. Assume that the electromagnetic wave emitted by the radar gun has a frequency of 9.0 109 Hz.

Find the magnitude of the difference between the frequency of the emitted wave and the wave that returns to the police car after reflecting from the speeder's car.

___________Hz

Answer 1

Try
Delta f = fv/c

where f=transmitted frequency
v=difference in velocity
c=velocity of light