Question

A policeman uses a radar gun to detect the speed of drivers in a 65 mph (29.06 m/s) zone. The gun uses sound waves with a frequency of 875 Hz. As one driver approaches, the echo’s frequency is 1020 Hz. What is the driver’s speed? Is the driver breaking the speed limit? state each equation

Answer 1

frequency emitted by radar fo = 875 Hz

speed of driver = v

speed of sound vs = 343 m/s

echo's frequency received f2 = 1020 Hz

frequency received by driver f1 = f0*(vs + v)/vs

as the driver hits the incoming wave , he is a moving observer

as it throws the pulse back , it is a moving source and the police man is receiver

echos frequency received by police f2 = f1*vs/(Vs-v)

f2 = f0*(Vs + v)/(Vs - V)

1024 = 875*(343 + v)/(343 - v)

speed of driver v = 27 m/s

he is not breaking the limit