How Does the Doppler Effect Alter Wavelength as a Train Approaches?

[astronomystudent]

1.) Suppose the sound from an approaching train whistle normally has a frequency of 1200 cycles per second, but the train is approaching at 50 meters per second. How would the Doppler Effect change the wavelength of the sound? (speed of sound 335 meters per second; I would like a quantitative answer here for full credit)

So far I have done the following: c = wavelength (frequency)
335 = wavelength (1200)
335/1200 = wavelength
wavelength = .279
wavelength = 2.79 x 10^-1 meters

c = wavelength (frequency)
335 = wavelength (1200 + 50)
335/1250 = wavelength
wavelength = .268
wavelength = 2.7 x 10^-1 meters

These are the forumlas I have from class, but I don't know any other way to solve the problem or if it is right.

 

[member 553083]

The Doppler Effect would change the wavelength of the sound from 2.79 x 10^-1 meters to 2.7 x 10^-1 meters.