A light-rail commuter train blows its 200 Hz horn as it approaches a crossing. The speed of sound is 339 m/s. (a) An observer waiting at the crossing receives a frequency of 220 Hz. What is the speed of the train? m/s (b) What frequency does the observer receive as the train moves away? Hz

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JemdetNasr JemdetNasr · Answer 1 · 2019-08-22T11:26:32+02:00

Answer:

a) 30.82 m/s

b) 183.33 Hz

Explanation:

a)

V = speed of the sound = 339 m/s

v = speed of the train = ?

f' = observed frequency by the observer = 220 Hz

f = actual frequency of the observer = 200 Hz

using the equation

[tex]f' = \frac{fV}{V - v}[/tex]

[tex]220 = \frac{(200)(339)}{339 - v}[/tex]

v = 30.82 m/s

b)

V = speed of the sound = 339 m/s

v = speed of the train = 30.82 m/s

f'' = observed frequency by the observer as train moves away = ?

f = actual frequency of the observer = 200 Hz

using the equation

[tex]f'' = \frac{fV}{V + v}[/tex]

[tex]f'' = \frac{(200)(339)}{339 + 30.82}[/tex]

f'' = 183.33 Hz