Easy/fustrating doppler queston - rather urgent 1. The problem statement, all variables and given/known data A swimming duck paddles the water with its feet once per time interval of 1.4 , producing surface waves with this period. The duck is moving at constant speed in a pond where the speed of surface waves is 0.31 , and the crests of the waves ahead of the duck have a spacing of 0.20 . a)What is the duck's speed? b)How far apart are the crests behind the duck? 2. Relevant equations f_d = f_s (v + v_d)/(v + v_s) 3. The attempt at a solution There are two things that I don't get. Is the duck the source or the detector of the waves? I think the duck is the source. Then f_s = 1/1.4 = 0.7142Hz The waves in the front will have f_d = 0.31/0.2 = 1.55Hz and v_d = 0.31m/s But what is the regular speed of the wave, v? Don't I ned that to solve for v_s?