Question

What is the frequency shift of a 79 GHz police radar signal when it reflects off a car moving at 110km/h ?

Answer 1

(delta f)/f = 2 v/c

v = 110 km/h = 30.5 m/s
c = 3.0^10^8 m/s
v/c = 1.02*10^-7
f = 79*10^9 Hz
Solve for delta f. It can be positive or negative, depending upon whether the car is approaching or receding.

This assumes the car is in front of or behind the radar gun. If is is off to the side, another formula must be used.