1. The problem statement, all variables and given/known data A listener L hears the siren from a moving police car ,S, which is moving away from the listener with a speed of v = 20.0 m/s. The listener is moving at 10.0 m/s towards the car. There is a wind blowing with a speed of v(wind)= 10.0 m/s from S to L. The siren is emitting sound at a frequency (f) of 800 Hz. The velocity of sound in air is 343 m/s. Calculate the frequency (f') heard by the listener and the wavelength (λ) of that wave. 2. Relevant equations f' = f(v +/- vD) / (v -/+ vS) v = fλ 3. The attempt at a solution Finding the new frequency is easy: f' = (800hz)(343+10+ 10)/(343+10+20) f' = 779 Hz. But now for finding the wavelength I'm confused. I know it's λ = v/f' but is it: v = 343m/s (the speed of sound in still air) v= 343+10 m/s (the speed of sound + the speed of the wind) v= 343+10+20 m/s (the speed of sound + the speed of the wind + the speed of the source) or something else? Any help would be much appreciated.