Police radar speed guns measure a car's speed using:

  1. the car's engine noise
  2. the brightness of the car
  3. the Doppler shift of reflected radio (microwave) waves
  4. the time for sound to travel
Answer

C) the Doppler shift of reflected radio (microwave) waves

Shift ∝ speed. SLO P-11-D-04 · Understanding

Physics MCQ · More Wave Intensity and the Doppler Effect MCQs · Practise