# Doppler Shift question

1. Apr 18, 2004

### Format

A train moving toward a detector at 31m/s blows a 305-Hz horn. What frequency is detected by a statiory train?

Using the equation f´= f(V + Vd/ V - Vs)

The answer is supposed to be 340-Hz but I don't understand how to get it. Mind helping me out?

2. Apr 18, 2004

### Format

anyone know?

3. Apr 18, 2004

### outandbeyond2004

I do not recognize the formula. My scientific encyclopedia gives this for the source approaching the detector:

$$f' = f(\frac{1}{1-\frac{v}{v_s}})$$

where v_s is the speed of sound in air.