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~christina~

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## Homework Statement

A siren mounted on the roof of a firehouse emits sound at a frequency of 900Hz. A steady wind is blowing with a speed of 15.0m/s. Taking the speed of sound in calm air to be 343m/s, Find the wavelength of the sound

a) upwind of siren

b) downwind of siren

Firefighters are approaching the siren from different directions at 15.0m/s. What frequency does a firefighter hear

c) if she is approaching upwind position so that she is moving in the direction in which the wind is blowing and

d) if she is approaching from a downwind position and moving against the wind?

## Homework Equations

Not sure but:

[tex] \lambda ' = \lambda - \Delta \lambda = \lambda - (v_s/ f) [/tex]

[tex] f'= v'/ \labmda= (v+ v_o)/ \lambda [/tex]

[tex] f'= ([v-v_o] / v)f [/tex] => observer moving away from source

[tex] f'= ([v+v_o] / v)f [/tex]= > observer moving toward source

[tex] f'= (v / [v-v_o] )f [/tex] => source moving toward observer

[tex] f'= (v / [v-v_o] )f [/tex]=> source moving away from observer

general...

[tex]f'= (v + v_o)/ (v-v_s) [/tex] => general doppler equation

## The Attempt at a Solution

a) I'm not sure about exactly what "wind" is considered but I think I know that it affects sound waves. (confused about source and observer situation with wind blowing)

I think that if wind is blowing toward the firehouse where the siren is emmitting sound then it should decrease the wavelength of the sound wave going toward the direction the wind is blowing (upwind I think)

And if you are facing away from the wind (downwind?) then the wavelength would be larger right?

would I use these equations:

[tex] f'= (v / [v-v_o] )f [/tex] => source moving toward observer

[tex] f'= (v / [v-v_o] )f [/tex]=> source moving away from observer

then find f' and then use that to find the wavelength?

with: [tex] f'= v'/ \labmda= (v+ v_o)/ \lambda [/tex]

I need help on this.

Thanks

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