Question

While standing on 3rd street you hear an approaching ambulance. Its siren oscillates in frequency between about 650 Hz and 750 Hz.

Later on as you near your destination, you come upon the scene of the accident. The now-stationary ambulance runs its siren as it's about to drive off. This time, you hear its pitch oscillate between 637.65 Hz and 735.75 Hz.

Using your physics knowledge, you estimate the speed that the ambulance must have been traveling while en route to the scene of the accident. How fast was it traveling? (Assume it's an average day where the speed of sound is about 343 m/s.)

A. 25 m/s (about 55 mph)

B. 18 m/s (about 40 mph)

C. 13 m/s (about 30 mph)

D. 9 m/s (about 20 mph)