Answer:
322 Hz
Step-by-step explanation:
v = speed of train approaching the railroad crossing = 80 km/h = 80 x 1000/3600 m/s = 22.22 m/s
V = speed of sound of the horn of train = 331.5 m/s
f = actual frequency of the sound from the horn = 300.0 Hz
f' = observed frequency of the horn
Using Doppler's effect, observed frequency is given as
f' = V f/(V - v)
inserting the values
f' = (331.5) (300.0)/(331.5 - 22.22)
f' = 322 Hz