Wavelength of sound affected by the moving observer?

[desmond iking]

Homework Statement

why the wavelength of sound is affected by the moving observer? because as the observer move, the sound source is still stationary . so in my opinion it's not affected by the moving observer. the ans is C for this question. i can't understand.

Homework Equations

The Attempt at a Solution

 

[Nathanael]

The source is still "stationary" but you could easily change your perspective so that you are "stationary" and then the source would be moving.

In other words, it is only relative velocity that is important (because one frame of reference is not better than the other)