If the listener does not move
Doppler:
Fl = { v/(v+vs) ] Fs
Fl is frequency heard
Fs is source frequency
vs = speed of source AWAY from listener
v = speed of sound
here:
when it is coming at you
FL = [345/(345-vs) ] 450
going awy:
Fl = [ 345/(345+vs) ] 450
so
22= 345*450 / [1/(345-vs) -1/(345+vs)]
1.417*10^-4 = [345+vs -345 +vs]/(345^2-vs^2)
1.417*10^-4 = [2 vs]/(345^2-vs^2)
I am going to say 345^2 >> vs^2
then
vs = 8.43 m/s
A fire truck emitting a 450 Hz signal passes by a stationary detector. The difference in frequency measured by the detector is 58 Hz. If the speed of sound is 345 m/s, how fast is the fire truck moving?
The answer should be 22 m/s but I don't even know where to start. Could there not be two answers?
1 answer
3 answers