## Essential University Physics: Volume 1 (3rd Edition)

We use the equation for the velocity considering the Doppler effect: $v = \frac{c\Delta f}{2f} = \frac{(10.8\times10^8 \ km/h)(15.6\times10^3 \ Hz)}{2(70\times10^9 \ Hz)} = 120 \ km/h$ The judge should rule in favor of the police officer, for this is the same as the recorded speed.