An ambulance has a siren that produces sound at a fixed frequency. The ambulance is travelling straight towards a stationary observer. As the ambulance gets closer to the observer, it slows down, and after it has gone past the observer, it speeds up. How does the frequency of the sound heard by the observer change while the ambulance is approaching and while it is moving away from the observer?
Physics 9702 · AS & A Level · Doppler effect for sound waves