Apolice car is parked by the side of a highway and it’s siren emits a sound measuring 750hz. as you approach the police car from a distance, you hear a change in the sound. the change in the sounds

The frequency of the sound increases

Explanation:

This phenomenon is known as Doppler effect, and it occurs when the observer is moving relative to the source of the sound (as in this case, sine you are moving towards the police car).

When you are moving towards the source of the sound, the frequency of the siren appears to increase, according to the formula:

where

f' is the apparent frequency of the sound

v is the speed of the sound wave

is the speed of the observer relative to the source, and it is positive if the observer is approaching the source, or negative if the observer is moving away

f is the real frequency of the sound (in this case, 750 Hz)