-01-, East Central Universty-PM. × East Central University-PHYS- n 12 of 12 Sapl

Question

-01-, East Central Universty-PM. × East Central University-PHYS- n 12 of 12 Sapling Learning Ma 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 8.27 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 9.07 kHz. Is the ambulance moving toward or away from you? O away O toward At what speed is the ambulance traveling? Number mph

Explanation / Answer

Since the observed frequency is more than the real frequency, thus the
ambulance is moving towards you.

f = fo•(V + Vr)/(V + Vs) Doppler
Vr +ve if rcvr moving toward srce; Vs -ve if srce moving toward rcvr

so here
9.07 kHz = 8.27kHz*(768 + 0) / (768 - Vs) for Vs in mph.   [W have
taken the speed of sound to be 768 mph]
This solves to
Vs = 67.74 mph

Hope this helps!

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