Question

Juan is standing on the street. An ambulance moves toward him and then passes by.

What best describes the pitch that Juan hears?

The pitch remains constant as the ambulance moves toward and then away from Juan.
The pitch increases and decreases in a repeated pattern as the ambulance passes Juan.
The pitch drops to a lower pitch once the ambulance passes by Juan.
The pitch increases to a higher pitch once the ambulance passes by Juan.

Answer 1

The pitch drops to a lower pitch once the ambulance passes by Juan.

Reason: by the Doppler effect a sound source moving toward an observer is heard at a higher frequency (higher pitch) and once it passes and moves away the observed frequency becomes lower.