—(away from A) at a speed of 35.0m/s. A listener is between the two whistles and is moving toward the right with a speed of 15.0m/s. No wind is blowing. a) What is the frequency from A as heard by the listener? b) What is the frequency from B as heard by the listener? c) What is the beat frequency detected by the listener?
(there are no question mark”?” in the right (away from A) is the continuations ty…)
this is doppler effect.
v=velocity of wave in medium=343m/s
vl=velocity of listener(+ if listener moving towards the source and – if moving away from source)
vs=velocity of source(+if source moving away from observer and – if source moving towards observer)
fa can be found.
fb can be found.
with respect to A the listener is opening the distance at 15 m/s
F = Fo ( V / ( V + Vl )
where V is speed of sound and Vl is relative speed of listener
F = 392 ( 343 / (343+15) = 375.6
with respect to B the source is moving away from the listener at 20 m/s
F = Fo ( ( V – Vs ) / V
where Vs is the speed of the source
F = 392 ( (343-20) / 343 ) = 369.1
the difference gives 6.5 beats/sec