Re: Solving for Stiffness using a plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg99971] Re: Solving for Stiffness using a plot*From*: dh <dh at metrohm.com>*Date*: Wed, 20 May 2009 05:02:43 -0400 (EDT)*References*: <guu2cm$65p$1@smc.vnet.net>

Hello, your problem is not well posed. As you write it, k is a function of the difference of x1 and x2: k[x1[t]-x2[t]]. But you only give equations for x1 and x2, your system is under defined. Further, k would be a functional and you do no more have an ordinary differential equation. On the other hand, if k is a constant and you mean: k (x1[t]-x2[t]), there is still an equation for k missing. Daniel twoseat wrote: > 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! >