Answer:
it seem that when car approaching toward the waiting car the radio frequency seem to be high and it seem to be low if moving away from the waiting car.
Explanation:
when waiting at traffic light to go green and listening radio station at particular frequency and then a car with playing same radio station and passing with constant speed then it seem that when car approaching toward the waiting car the radio frequency seem to be high and it seem to be low if moving away from the waiting car.