A train moving at 30 m/s toward a stationary observer emits a 500 Hz whistle. If a wind of 10 m/s blows from the train toward the observer, what is the observed frequency?
Correct: A
Effective speed of sound becomes v' = 343 + 10 = 353 m/s. Observed frequency is f' = f(v' + vo)/(v' - vs) = 500(353)/(353 - 30) ≈ 548 Hz.