Doppler effect wavelength from car

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Homework Help Overview

The discussion revolves around a problem involving the Doppler effect, specifically focusing on a car traveling at a certain speed with a siren emitting sound waves. Participants are tasked with finding the wavelength of the sound waves in different positions relative to the car and the frequency perceived by a stationary observer.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the Doppler effect and the relevant equations, with some questioning the definitions of variables in the provided formula. There are attempts to calculate the wavelength based on the car's speed and the frequency of the siren, as well as discussions on how to approach the problem of finding the frequency heard by a stationary observer.

Discussion Status

Some participants have made attempts to calculate the wavelengths for sound waves in front of and behind the car, using equations from their textbooks. There is an ongoing exploration of how to derive the frequency from the calculated wavelengths, but no consensus has been reached on the overall approach or final answers.

Contextual Notes

Participants note uncertainty regarding the definitions of variables in the equations and the implications of the car's motion on the sound waves. There is also mention of the need to clarify the velocity of sound in the medium and how it relates to the source's velocity.

matt_crouch
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Homework Statement



A car is traveling at 30m/s in still air. the frequency of the siren on the car is 600hz. The velocity of sound in still air is 330 m/s. what is the wavelength of the sound waves

a)directly in front of the car
b)directly behind the car

What is the frequency of the sound heard by a stationary observer

c)directly in front of the car
d)directly behind the car

Homework Equations



FD=CD/Cs *Fs


The Attempt at a Solution



Im not really sure where to start if someone could point me in the right direction.

Cheers
 
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matt_crouch said:

Homework Statement



A car is traveling at 30m/s in still air. the frequency of the siren on the car is 600hz. The velocity of sound in still air is 330 m/s. what is the wavelength of the sound waves

a)directly in front of the car
b)directly behind the car

What is the frequency of the sound heard by a stationary observer

c)directly in front of the car
d)directly behind the car

Homework Equations



FD=CD/Cs *Fs


The Attempt at a Solution



Im not really sure where to start if someone could point me in the right direction.

Cheers

OK, let's kick this off. Can you first get the frequency of the doppler shifted sound wave? I think your equation above (though you haven't defined what each variable represents) should tell you that.
 
jamesmo said:
OK, let's kick this off. Can you first get the frequency of the doppler shifted sound wave? I think your equation above (though you haven't defined what each variable represents) should tell you that.

Also, write out how to get your C's.
 
well i can find the wavelength of the car but i think its only when its stationary I am not sure

If Cs of the source is 30 m/s an the frequency is 600 hz
then the wavelength is

0.05 m

but I am not so sure where to go from there.. if i have Cs and Fs how do i find what the wavelength in front and behind is
 
actually i think i have the answer.. i used an equation that was stated in my textbook..

Wavelength behind = (vm+us)/Fs

where Vm= velocity of sound in medium
Us= velocity of source


and it gets an answer of 0.6 m

and

wavelength infront = (vm-us)/Fs

given an answer of 0.5 m

and from here i can calculate the frequency of each wavelength from V= F*(Lambda)
 
matt_crouch said:
actually i think i have the answer.. i used an equation that was stated in my textbook..

Wavelength behind = (vm+us)/Fs

where Vm= velocity of sound in medium
Us= velocity of source


and it gets an answer of 0.6 m

and

wavelength infront = (vm-us)/Fs

given an answer of 0.5 m

and from here i can calculate the frequency of each wavelength from V= F*(Lambda)

Awesome! Have a good one.
 

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