ROGER F. answered • 07/18/15

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DR ROGER - TUTOR OF MATH, PHYSICS AND CHEMISTRY

**The answer is a**. The observed frequency (fo, you could call it "pitch") decreases. The velocity of sound is its (frequency*wavelength), (i.e. #waves per sec*length of a wave = distance per sec = velocity), so if f decreases, wavelength increases, because the velocity of sound is constant, even if the source is moving.

The formula for the frequency of sound emitted by an object moving away from a stationary observer, is

*observed*(fo) to be:fo = fs[1/(1 + Vs/V) where fs is the frequency at the source, Vs is velocity of moving object, and V is the velocity of sound.