A student stands at a railroad crossing and records the frequency of a train’s whistle (rest frequency 440 Hz) once each second as the train moves past on a straight track at constant speed. Her data are shown below.
Time (s): −3 −2 −1 0 1 2 3
Observed f (Hz): 480 466 453 440 428 416 405
Assuming still air and a speed of sound of 340 m/s, which of the following is closest to the train’s speed?
a) 15 m/s
b) 31 m/s
c) 28 m/s
d) 43 m/s