Final answer:
The subject of this question is the Doppler effect in the context of sound waves. The Doppler effect is the observed change in frequency of a wave when there is relative motion between the source of the wave and the observer.
Step-by-step explanation:
The subject of this question is the Doppler effect in the context of sound waves. The Doppler effect is the observed change in frequency of a wave when there is relative motion between the source of the wave and the observer. In this case, the question is asking about the change in frequency of a police siren as it emits a sound wave with a frequency of 1600 Hz.