The Doppler shift formula fo = fs vv pm vs assumes that:

  1. the air moves with the source
  2. the source is stationary
  3. the speed of sound changes
  4. the observer is stationary relative to the air
Answer

D) the observer is stationary relative to the air

Moving-observer case is not required. SLO P-11-D-03 · Application

Physics MCQ · More Wave Intensity and the Doppler Effect MCQs · Practise