1. The problem statement, all variables and given/known data A source of sound emits waves of wavelength λ, period T and speed v when at rest. The source moves away from a stationary observer at speed V, relative to the observer. The wavelength of the sound waves, as measured by the observer is A. λ + vT B. λ - vT C. λ + VT D. λ - VT 2. Relevant equations f' = f(v / (v±u) moving source f' = f((v±u) / v) moving observer 3. The attempt at a solution Since the source is moving away, it is safe to say assume that the frequency would be lower as the wavelengths emitted from the moving source would become more and more apart. Therefore f' < f of moving source. But up till here, I am lost...Please explain! I want to understand this question. Cheers.