Wave speed, freq, and period of wave on a string

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Homework Help Overview

The discussion revolves around a problem involving wave properties on a guitar string, specifically focusing on wave speed, frequency, and period. The scenario includes a string of known length, tension, and linear mass density, with specific points where the string is fretted and plucked.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations of wave speed, frequency, and period based on the given parameters. There are questions regarding the assumptions made about the wavelength and whether the calculations reflect the conditions after the fingers are removed from the string.

Discussion Status

The discussion is ongoing, with participants clarifying the problem requirements and questioning the assumptions made about the wavelength and the impact of the fretting fingers on the wave properties. Some guidance has been offered regarding the interpretation of the setup.

Contextual Notes

There is a noted discrepancy in the understanding of how the length of the string and the positions of the fingers affect the wavelength and subsequent calculations. The original poster has acknowledged potential errors in their approach.

dinospamoni
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Homework Statement



A musician frets a guitar string of length 1.5 m at x = 0.34 m with one finger, and simultaneously plucks the string at x = 0.17 m with another finger (raising it to a height h = 2.1 mm. Both fingers are simultaneously removed from the string, and it is allowed to vibrate. The string has a tension of 76 N, and a linear mass m = 4.9 g/m.

Homework Equations



[itex]v=\sqrt{\frac{T}{\mu}}[/itex]
where
[itex]\mu=\frac{mass\,in\,kg}{Length\,in\,m}[/itex]

[itex]v=f\lambda[/itex]



The Attempt at a Solution



I started off converting the linear mass:

[itex]4.9\frac{g}{m} \times\frac{1 kg}{1000 g} = .0049\frac{kg}{m}[/itex]

Then I plugged that into the equation:

[itex]v=\sqrt{\frac{76 N}{.0049\frac{kg}{m}}}[/itex]

and got v=124.54 m/s

From here I used [itex]v=f\lambda[/itex]
where [itex]\lambda=.68 m[/itex]

and got frequency = 183.147 Hz

Taking the reciprocal of that:

Period = .00546 s

These aren't the right answers, but I don't see where I went wrong

Also, picture attached
 

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You don't say exactly what is being asked. You have calculated, correctly I believe, the period as though the fret finger is still in place, but is it what was asked for?
 
I included what was asked for in the title, but forgot to include it in the question. It's asking for the wave velocity, frequency, and period.

I accounted for the finger being lifted off by making the wavelength twice the interval between the finger and the origin. Is that not right?
 
dinospamoni said:
I included what was asked for in the title, but forgot to include it in the question. It's asking for the wave velocity, frequency, and period.

I accounted for the finger being lifted off by making the wavelength twice the interval between the finger and the origin. Is that not right?
No, that's what it would be if the finger were left in place. But even then, 1.5m is not twice 0.34m. How do you propose to bring 1.5m into the equation?
 

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