Doppler Effect: Train A and B Whistle Frequency Calculation

[lc99]

Homework Statement

Two trains A and B have a whistle that blows at a frequency fT = 392 Hz. Train A is stationary and train B is moving toward the right (away from A) at a speed of vB = 35 m/s. A listener is between the two trains and is moving toward the right with a speed of vL = 15 m/s. No wind is blowing and assume the speed of sound v = 344 m/s. What is the beat frequency fbeat detected by the listener?

Homework Equations

fL = fS [ ( V + Vl ) / (V + Vs) ]
V = 344 m/s

The Attempt at a Solution

for frequency of L by train B -
fL = 392 [ (344 - 15)/(344 +35) ] = 371.3

for train B
fL = 392 [ (344-15) / 344 ] = 374.91

375-371 = 4 = fbeat

 

[tnich]

Homework Statement

Two trains A and B have a whistle that blows at a frequency fT = 392 Hz. Train A is stationary and train B is moving toward the right (away from A) at a speed of vB = 35 m/s. A listener is between the two trains and is moving toward the right with a speed of vL = 15 m/s. No wind is blowing and assume the speed of sound v = 344 m/s. What is the beat frequency fbeat detected by the listener?

Homework Equations

fL = fS [ ( V + Vl ) / (V + Vs) ]
V = 344 m/s

The Attempt at a Solution

for frequency of L by train B -
fL = 392 [ (344 - 15)/(344 +35) ] = 371.3

for train B
fL = 392 [ (344-15) / 344 ] = 374.91

375-371 = 4 = fbeat

Looks right to me.