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I've been trying to solve this question from Goldstein's Classical Mechanics.

The picture I have of the question is from a later edition and the hint was removed from the question, the hint was let

η_{3}=ζ_{3}

η_{1}=[itex]\frac{ζ_{1}+ζ_{5}}{\sqrt{2}}[/itex]

η_{5}=[itex]\frac{ζ_{1}-ζ_{5}}{\sqrt{2}}[/itex]

What I have done is first let each particle be represented by a displacement x1...x5,

Then wrote out T = 1/2m([itex]x^{2}_{1}+x^{2}_{3}+x^{2}_{5}[/itex]) + 1/2M([itex]x^{2}_{2}+x^{2}_{4}[/itex])

and V = k/2 *( [itex] x_{i}-x_{j}-b[/itex] ) i = 2..5, j = 1..4 i≠j

so V = k/2 *( [itex]x_{2}-x_{1}-b[/itex] ) + k/2(....) up to i = 5 j = 4

then Since η = x - dx the system is at equilibrium when

b = dx_{2}- dx_{1}= dx_{3}- dx_{2}= .... up to i = 5 j = 4

then V = 1/2k (η_{2}- η_{1}) + ... up to i = 5 j = 4

Then I subbed in the hints it provided and also as one of the hints says treat the normal co-ords of 2 and 4 as symetric I let η_{2}=ζ_{2}=-η_{4}

Some stuff cancelled and I ended up with

V = k/2 *( [itex]ζ^{2}_{1}+ζ^{2}_{2}+ζ^{2}_{5}-2\sqrt{2}ζ_{2}ζ_{5}[/itex] )

I turned it into a matrix which was (this is where I start stuffing up I think)

...............1.....0......0 (sorry had to use the ... to make the matrix look kind of like a matrix)

V = k/2.....0.....4....sqrt2

...............0..-sqrt2..1

Then since there were only varibles of 1, 2 and 5 I turned T into

..............m 0 0

T = 1/2...0 M 0

..............0 0 m

Then did the usual thing for eigenvalues |V-ω^{2}T|=0

One was pretty ugly, one was sqrt(k/m), and the last one I had trouble finding because it was a mess of a cubic.

I decided to put the question at the bottom so the add didn't squish it,

http://img193.imageshack.us/img193/7747/asdasddh.jpg [Broken]

Is what I did alright? The part I'm not confident about at all is when i turn V into a matrix, and the book they also drop the 1/2 for both V and T which I didn't really understand why.

Thanks in advanced for any help.

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# Homework Help: Coupled Oscillator

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