Question

You are walking along a small country road one foggy morning and come to an intersection. While you are crossing, you hear an ambulance siren. As a paramedic, you know that the siren sounds at a frequency of 5.87 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 5.07 kHz. Is the ambulance moving toward or away from you?

Answer 1

Oroginal frequency is F = 5.87 kHz , but the apparent frquency heard by stationary listener is f = 5.07 kHz , that is the frequency heard is less than the actual frquency. Thius implies that number of cycles of sound waves reaching the listener is less than that when the ambulance is stationary. This implies that the ambulance is moving away from the listener so that it takes more time than actual for the next cycle to reach after one cycle has reched the listener.