Q) You are standing at the side of the road. An ambulance approaches you with its siren on. As it approaches, you hear a frequency of 460Hz. As it moves away, 410Hz.
If the hospital is 3km away, estimate the time taken for the ambulance to reach the hospital, assuming it keeps a constant velocity,
Doppler Effect Watch
- Thread Starter
Last edited by Feynboy; 05-10-2016 at 21:58.
- 05-10-2016 20:19
- 06-10-2016 00:00
question asks for an estimate so IMO you can cut some corners
c=330 m/s (speed of sound)
ambulances typically travel much slower than the speed of sound (IME)
split the difference of the frequencies to get a frequency f perceived by the ambulance driver = f0 435Hz
use an approximate formula
to get the speed of the ambulance
Δf is the difference between the frequency the stationary observer hears and f[sub]0 (i.e. +ve if the observer hears an increased frequency)
Δv is the speed at which the source is approaching or receding from the observer (i.e. +ve if the source is getting closer to the observer)