일반물리학 1 — Waves-II: Problem 42

42 Two trains are traveling toward each other at 35.7 m/s relative to the ground. One train is blowing a whistle at 850 Hz. (a) What frequency is heard on the other train in still air? (b) What frequency is heard on the other train if the wind is blowing at 35.7 m/s toward the whistle and away from the listener? (c) What frequency is heard if the wind direction is reversed?