Lars is jogging besides the railroad tracks at a speed of 2.00m/s when he hears a train whistles behind him at a frequency of 2115Hz. if the actual frequency of the train whistle is 2000 Hz, how fast is the train moving

The given values on the problem are:

fo = 2000 Hz

f = 2115 Hz

v = 340 m/s

vo = - 2.00 m/s

Since vs, or the final speed of the train is asked, we used this equation:

f = fo (v+vo) / (v-vs)

Substituting the give values:

2115 = 2000 (340-2) / (340-vs)

By algebra:

vs = 20.4 m/s