Answer:
Kindly check explanation
Explanation:
Given the following :
As train approaches ; frequency, f1 = 94Hz
As train recedes; frequency, f2 = 71Hz
Speed of sound in air ; v = 340m/s
A) speed of sound source (speed of train) = vs
From doppler effect :
As the train recedes ;
f2 = fs [v / (v + vs)] - - - - (1)
As train approaches :
f1 = fs [v / (v - vs)] ----- (2)
To find vs equate (1) and (2)
fs [v / (v - vs)] = fs [v / (v + vs)]
f1/f2 = v / (v - vs) ÷ v / (v + vs)
f1 / f2 = v / (v - vs) × (v + vs) / v
f1 / f2 = (v + vs) / (v - vs)
Let f1 / f2 = f
f = (v + vs) / (v - vs)
f (v - vs) = v + vs
fv - fvs = v + vs
fv - v = vs + fvs
v(f - 1) = vs(1 + f)
v(f - 1) / (1 + f) = vs
B)
v(f - 1) / (1 + f) = vs
f = f1 / f2 = 94/71 = 1.32 Hz
340(1.324 - 1) / (1 + 1.324) = vs
vs = 340(0.324) / 2.324
vs = 110.16 / 2.324
vs = 47.40 m/s
C.) To calculate fs, frequency of train, substitute vs into our equation.
f2 = fs [v / (v + vs)]
Following our substitikn we obtain:
fs = (2f / (f + 1))f2
D)
fs = (2f / (f + 1))f2
fs = 2(1.324) / (1.324 +1)) × 71
fs = (2.648 / 2.324) × 71
fs = 1.1394148 × 71
fs = 80.898450
fs = 80.90 Hz
