Two train whistles, A and B, each have a frequency of 392 Hz. A is stationary and B is moving toward the right?

Question

---(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 frequency from A as heard by engineer inside train B?
Two train whistles, A and B, each have a frequency of 392 Hz. A is stationary and B is moving toward the right? ---(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 frequency from A as heard by engineer inside train B?

Explanation / Answer

this is doppler effect.
observed frequency=f=((v+vl)/(v+vs))*fo
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)
a)v=343,
vl= -15
vs=0
f0=392
fa can be found

fa= 392 ( 343 / (343+15) = 375.6

b)v=343
vl=15
vs=35
f0=392
fb can be found

fb = 392 ( (343-20) / 343 ) = 369.1

c)frequency of a wrt b

f = 392*(343-35/343)=352hz

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