1. The problem statement, all variables and given/known data A sound source emits sounds of frequency 210 Hz that travel through still air at 340 m/s. The listener moves at 85 m/s relative to still air toward the stationary source. What is the wavelength of the sound between the source and the listener? 2. Relevant equations f' = f[1+ Vlistener/Vsound] v=(wavelength)f 3. The attempt at a solution well using the doppler effect since the listener is moving towards the stationary source i know it will be f'=f[1+Vlistener/Vsound] i find the f' right... but when using v=wavelength*frequency, which frequency do i actually use. because i know although im solving for f' , im just wondering if its a trick or something because i'm a little confused on the concept. so for f' i get 262.5 Hz then i plug it in to the v=wavelength*freq , but which velocity do i use? the speed of sound or the speed of the listener moving? using the speed of sound i get 340 m/s = wavelength * 262.5 and end up with 1.295m as the wavelength.