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Wave on a string under tension 
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#1
Mar912, 04:20 AM

P: 180

1. The problem statement, all variables and given/known data
A pulse takes 0.1s to travel the length of a string. The tension in the string is provided by passing the string over a pulley to a weight which has 100 times the mass of the string. What is the length (L) of the string? What is the equation of the third normal mode. 2. Relevant equations v=√(F/u) u=m/L 3. The attempt at a solution We have L/t = √(100.m.g/(m/L) where g = surface gravity So 100L^2 = 100gL so L= magnitude(g) = 9.8 m This type of question was not covered directly in our notes and I am unsure if my working is correct. Thanks for any help. 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution 


#2
Mar912, 04:48 AM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 12,395

Welcome to PF.
Reasoning seems fine to me  notice how the number end up all nice? Did you do the next bit? 


#3
Mar912, 05:00 AM

P: 180

It was the simplicity in the final answer that made me doubt it.
Thank you, but what is LQ? y_3 = (A_3)sin(n.pi.x/L)cos((w_n)t) We have 1.5 waves in a time of 0.1s. So w = 30.pi radians I don't see how I can get the amplitude. So y = A sin(3.pi.x/9.8)cos(30.pi.t) 


#4
Mar912, 05:01 AM

P: 180

Wave on a string under tension
(where w is angular frequency)



#5
Mar912, 05:19 AM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 12,395

angular frequency is radiens per second. Note: cannot comment on answers as such  only methods and reasoning. 


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