The speed of sound in air is about 660miles/hour. A passenger train approaches an unguarded railroad crossing at a constant speed of 60 miles/hour and the locomotive sounds its horn which has a frequency of 400 Hz.
[A]. What frequency does a listener standing near the crossing hear?
[B]. If the train continues past the crossing at the same speed, what frequency does the listener hear?
[C]. What frequency does a person riding on top of the last car hear? Why?