[SOLVED] Doppler Effect? 1. The problem statement, all variables and given/known data A bat flying at 4.0 m/s emits a chirp at 20 kHz. If this sound pulse is reflected by a wall, what is the frequency of the echo received by the bat? 2. Relevant equations Not sure. Do I use the f(1)=f*[(v+/-observer velocity)/(v+/-source velocity)] 3. The attempt at a solution Not sure where to start. I seem to remember something about sound waves being returned inverted if they hit a wall. Does this factor in?