- #1
ckelly94
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Homework Statement
So I'm given two horizontal masses coupled by two springs; on the left there is a wall, then a spring with k[itex]_{1}[/itex], then a mass, then a spring with k[itex]_{2}[/itex], and finally another mass, not attached to anything on the right. The masses are equal and move to the right with x[itex]_{1}[/itex] and x[itex]_{2}[/itex], respectively. I'm trying to find the normal modes of oscillation where k[itex]_{1}[/itex]=2k[itex]_{2}[/itex].
Homework Equations
As usual, we write the equations of motion for each of the masses, i.e.
[itex]\frac{d^{2}x_{1}}{dt^{2}}[/itex]+([itex]\omega_{1}^{2}[/itex]+[itex]\omega_{2}^{2}[/itex])x[itex]_{1}[/itex]-[itex]\omega_{2}^{2}[/itex]x[itex]_{2}[/itex]=0
and
[itex]\frac{d^{2}x_{2}}{dt^{2}}[/itex]-([itex]\omega_{2}^{2}[/itex])x[itex]_{1}[/itex]+([itex]\omega_{2}^{2}[/itex])x[itex]_{2}[/itex]=0
The Attempt at a Solution
The eigenvalues for this matrix are given by
([itex]\omega_{1}^{2}+\omega_{2}^{2}-\lambda[/itex])([itex]\omega_{2}^{2}-\lambda[/itex])-[itex]\omega_{2}^{4}[/itex]=0
At this point, I plugged k[itex]_{1}[/itex]=2k[itex]_{2}[/itex] into this mess and determined that [itex]\lambda_{1,2}[/itex]=-2[itex]\omega_{2}^{4}[/itex][itex]\pm(\omega_{2}^{2}\sqrt{8\omega_{2}^{2}+2}[/itex])
So did I do something wrong algebraically, or are the eigenvectors, and thus the normal modes of oscillation simply [itex]\lambda[/itex] [itex]\propto[/itex]
( [itex]\stackrel{\omega_{2}^{2}}{3\omega_{2}^{2}+2\omega_{2}^{4}+\omega_{2}^{2}\sqrt{8\omega_{2}^{2}+2}}[/itex] ) ?
PS: Sorry about the formatting. I wasn't sure how to make a matrix, but the last line should be a matrix.
Thanks in advance!