The document discusses the Doppler effect as it relates to the change in frequency of sound from an ambulance siren observed by a pedestrian. It provides the original frequency of the siren as 700 Hz and speed of the ambulance as 70 km/h. Using the Doppler effect formula to calculate the observed frequency based on the ambulance moving away from the pedestrian, the summary is: The Doppler effect causes the frequency of an ambulance siren with a frequency of 700 Hz travelling at 70 km/h away from a pedestrian to be observed as 662 Hz.
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).
