Fg = 440 Hz = Freq. of the generator.
Vg = 40 m/s = Velocity of the generator.
Vs = 343 m/s = Velocity of sound.
Vr = 0 = Velocity of the receiver(person
listening to the sound).
Fr = ((Vs+Vr)/(Vs-Vg))*Fg
Fr = ((343+0)/(343-40))*440 =
(343/303)*440 = 498.1 Hz. = Freq. heard by the receiver.
Note: When the sound generator is approaching you, the frequency heard is
higher than the generated frequency.
Therefore, we use a positive (+) sign in
the numerator and a negative sign in the
denominator.
When the generator is leaving you, reverse both signs.
A friend plays an A note (440 Hz) on her piccolo while running towards you at 40 m/s. What frequency do you hear just before she runs into you?
-I am not sure where to start on this problem. I wrote down the givens: fs=440 hz, vs=40 m/s, v=343 m/s. and I'm trying to solve for FL. So FL=Fs(v+vL/v+vs) right? except there is no vl…so I tried FL=Fs(1/1-vs/v) but it came out all jumbled in my calculator… I don't know how to proceed.. Any help would be appreciated! :) Thanks!
1 answer