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Waves: String Physics? Correct my units

  • Thread starter pugfug90
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Waves: String Physics?? Correct my units..

Homework Statement


The velocity of a wave on a string depends on how hard the string is stretched and on the mass per unit length of the string. If T is the force exerted on the string and Mu is the mass/unit length, then velocity v is

http://nas.cl.uh.edu/blanford/FormulasWaves_files/image012.gif [Broken]
(I think)

A piece of string 5.3m long has a mass of 15g. What must the force on the string be to make wavelength of a 125Hz wave 120cm?

Homework Equations





The Attempt at a Solution


The given answer is 63.7N

I converted wavelength lambda to 0.12M and 15g to 0.015kg..
wavelength=velocity/frequency.. so wavelength*frequency=velocity..
0.12M*125Hz=15 m/s=velocity

15m/s = [square root of T(force)/Mu(mass length ratio)]
He also gave us another equation..
instead of [square root T/Mu], there is also [square root T*length/mass]

So..
15m/s=[square root of T*5.3m/0.015kg]
[(15^2 m^2)(0.015kg)]/[(s^2)(5.3m)]=T..
T=~0.636N..which would be right if it were multiplied by 100.. Anyone see where I went wrong?
 
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Answers and Replies

  • #2
Kurdt
Staff Emeritus
Science Advisor
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120 cm is 1.2 meters not 0.12 meters.
 
  • #3
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Har harrr
Oopss and thanks!
 

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