Solving for Stiffness using a plot

• To: mathgroup at smc.vnet.net
• Subject: [mg99896] Solving for Stiffness using a plot
• From: twoseat <caseyktimmons at gmail.com>
• Date: Tue, 19 May 2009 06:41:30 -0400 (EDT)

```Hello

I am trying to use mathematica to solve for the stiffness of a spring system but I cannot figure out how to plot my equations correctly.

I have:
m1=220;
m2=300;
v0=12;
k; (*temp. I am solving for this*)

a = NDSolve[{k[x1[t] - x2[t]]*(x1[t] - x2[t]) - m1*x1''[t] == 0,
m1*x1''[t] - m2*x2''[t] == 0,  x1[0] == 0,  x2[0] == 0,
x1'[0] == v0, x2'[0] == 0}, {x1[t], x2[t]}, {t, -10, 20}]
dis = Plot[Evaluate[{x1[t] - x2[t]} /. a], {t, -10, 20}]

This gives me multiple errors and wont plot.

I am going to try to plot k[x1[t]-x2[t]]*(x1[t]-x2[t]) vs (x1[t]-x2[t]) to solve for k but I can't determine how to set up my equations to plot.

Any help or recommendations would be appreciated!

```

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