Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

A car, moving at 85 mi/hr, passes a station-
ary police car whose siren has a frequency of
500 Hz.
What is the frequency change heard by an
observer in the moving car as he passes the
police car? The velocity of sound in air is
343 m/s . (1 mi = 1.609 km)
Answer in units of Hz.