When a source of sound passes us, whether it be a car horn or a train whistle, the pitch we hear goes from high to low. Explain why. Use any relation to support your explanation?

When a source of sound, e.g., car horn or a train whistle passess us, the observed pitch varies from high to low. This is due to Doppler’s effect. Initially the source, e.g., the car horn or a train whistle is approaching us, i.e., the source is approaching the observer at rest, then the observed pitch (v’) appears to be more than the true pitch (v) because v’