Help with part 2 please O 3/22/2017 09:00 AM A 1.5/2 Gradebook Print Calculator

Question

Help with part 2 please

O 3/22/2017 09:00 AM A 1.5/2 Gradebook Print Calculator Periodic Table Question 1 of 2 In Map Sapling Learning ma milan learning 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 6.67 kHz. But, as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 7.31 kHz. Is the ambulance moving toward or away from you? O toward away At what speed is the ambulance traveling? Number mph AD Give Up & View Solution Check Answer O Next Exit Previous Hint

Explanation / Answer

The frequency heard by person as paramedic taken as the frequency of the source (Ambulance). Then

Frequency of the source < Frequency heard by the person as musician

i.e better frequency you hear when the source approaching you.

The ambulance is moving towards you.

From the Doppler's effect for approaching source we can write as

f = [ v /(v -vs ) ] fs

here f =frequency heard by you as musician =7.31 kHz

fs =Ambulance frequency = 6.67 kHz

v= velocity of sound in air =768 mph

vs = velocity of ambulance

on substituting all values we get

7.31 kHz = [768 mph / ( 768 mph - vs )] (6.67 kHz)

[768 mph / ( 768 mph - vs )] = 1.09595

768 mph - vs = 700.76 mph

vs = 67.24 mph

Therefore the speed of the ambulance approaching you is 67.24 mph.

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