# Wave on a string under tension

by BOYLANATOR
Tags: string, tension, wave
 P: 102 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
 HW Helper Sci Advisor Thanks P: 9,091 Welcome to PF. Reasoning seems fine to me - notice how the number end up all nice? Did you do the next bit?
 P: 102 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)
P: 102

## Wave on a string under tension

(where w is angular frequency)
HW Helper
Thanks
P: 9,091
 but what is LQ?
A spelling mistake. Thanks.

angular frequency is radiens per second.
 I don't see how I can get the amplitude.
me neither.
 It was the simplicity in the final answer that made me doubt it.
I suppose with all the computer-randomized problems you get these days, nice numbers must be rare.

Note: cannot comment on answers as such - only methods and reasoning.

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