2. You are about to cross the street when you hear an
ambulance. The siren of the ambulance has a frequency of
700 Hz and is travelling at 70 km/h. What frequency would
you observe as the ambulance passes you?
• 742 Hz
• 660 Hz
• 662 Hz
• 739 Hz
3. Solution
• The speed of the ambulance is 70 km/h which
equates to 19.44 m/s. Using the below equation
we get f0=(700 Hz) ((343 m/s - 0m/s)/(343 m/s
+19.44 m/s))=662 Hz. Notice we use + in the
denominator since the ambulance passes us
(moving away from the receiver).
