Physics (AS & A Level) · May / June 2021 · Paper 11 · Question 24

An ambulance has a siren that emits sound of a constant frequency. The ambulance is moving directly towards a stationary observer. The ambulance decelerates as it is approaching the observer and then accelerates after it has passed the observer. How does the frequency of the sound heard by the observer change as the ambulance is approaching and as it is moving away from the observer?

1. Aapproaching observer: decreases; moving away from observer: decreases
2. Bapproaching observer: decreases; moving away from observer: increases
3. Capproaching observer: increases; moving away from observer: decreases
4. Dapproaching observer: increases; moving away from observer: increases

As printed in the paper