Introduction to SAT II Physics

A cop car drives at 30 m/s toward the scene of a crime, with its siren blaring at a frequency

of 2000 Hz. At what frequency do people hear the siren as it approaches? At what frequency

do they hear it as it passes? The speed of sound in the air is 343 m/s.

As the car approaches, the sound waves will have shorter wavelengths and higher
frequencies, and as it goes by, the sound waves will have longer wavelengths and lower
frequencies. More precisely, the frequency as the cop car approaches is:

The frequency as the cop car drives by is:

Key Formulas

Frequency

of Periodic

Oscillation

Speed of

Waves on a

String

Wave

Speed

Wavelengt

h for the

Harmonic

Series

Frequency

for the

Harmonic

Series

Beat

Frequency

Doppler

Shift