What is the Velocity of an Object if Soundwaves Behind it are 3 Octaves Lower?

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Homework Help Overview

The discussion revolves around a physics problem involving the velocity of an object in relation to sound waves. The scenario specifies that sound waves behind the object are three octaves lower than those in front, with the speed of sound given as 300 m/s.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to relate the wavelengths of sound waves in front and behind the object, suggesting a logarithmic relationship due to the octaves. Participants question the equations connecting speed and frequency, with some suggesting the use of Doppler effect equations.

Discussion Status

Participants are actively engaging with the problem, asking for clarification on relevant equations and discussing the relationship between frequency and wavelength. There is a mix of attempts to derive equations and requests for further elaboration on the concepts involved.

Contextual Notes

Some participants express uncertainty about the necessity of using Doppler effect equations, indicating a potential divergence in approaches to the problem. The discussion reflects varying levels of familiarity with the underlying physics concepts.

Anabell
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Homework Statement


Given the speed of sound in an environment, c = 300 m/s. We have an object moving with a ceratin velocity. If we know that the soundwaves behind the object are lower by 3 octaves than in front of it, then what is the velocity of the object?

2. Attempt at solving it.
I arrived at the conclusion that if the wavelength of the soundwaves in front of the object is x, then behind it is eight times of that (eg. x*8), since octaves are on a logaritmic scale. I don't know where to go on from here.
 
Last edited:
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Where are your equations relating speed to frequency.

You know that f1 = 8 f2, where f1 is the frequency in the front and f2 is the frequency behind.

Plug these into your equations relating speed to frequency, and you should be able to solve for the unknown rest frequency and velocity.
(Two equations and two unknowns.)
 
Dr. Courtney said:
Where are your equations relating speed to frequency.

You know that f1 = 8 f2, where f1 is the frequency in the front and f2 is the frequency behind.

Plug these into your equations relating speed to frequency, and you should be able to solve for the unknown rest frequency and velocity.
(Two equations and two unknowns.)
I don't have those equations, could you please ellaborate? :)

Do you mean speed = wavelength * frequency?
 
Last edited:
You must have Doppler effect equations relating speed and frequency shifts for sources moving toward and away.
 
Anabell said:

Homework Statement


Given the speed of sound in an environment, c = 300 m/s. We have an object moving with a certain velocity. If we know that the soundwaves behind the object are lower by 3 octaves than in front of it, then what is the velocity of the object?

2. Attempt at solving it.
I arrived at the conclusion that if the wavelength of the soundwaves in front of the object is x, then behind it is eight times of that (eg. x*8), since octaves are on a logarithmic scale. I don't know where to go on from here.
I don't think you need to use Doppler effect equations solve this.

If frequency, fB, is one octave above frequency, fA, then how is fB related to fA mathematically?
 

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