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Re: Help with solving ODE

• To: mathgroup at smc.vnet.net
• Subject: [mg81789] Re: Help with solving ODE
• From: Norbert Marxer <marxer at mec.li>
• Date: Wed, 3 Oct 2007 06:10:59 -0400 (EDT)
• References: <fdvdq7$sul$1@smc.vnet.net>

On 3 Okt., 08:45, Pioneer1 <1pione... at gmail.com> wrote:
> Hi,
>
> Can anyone help solve this linearized differential equation:
>
> Iy'' + ky' = 2GMmd/a^2
>
> Primes are time derivates of y (=theta=excursion angle). Is it
> possible to solve this for the initial conditions y(0)=0 and y'(0)=0?
>
> I got the solution at sci.math for the non-linear version and I want
> to compare the two. Here's the link to sci.math thread:
>
> http://groups.google.com/group/sci.math/browse_thread/thread/a6ee2f78...
>
> Further information is also available at sci.physics.research
>
> http://groups.google.com/group/sci.physics.research/browse_thread/thr...
>
> Parameters are:
>
> > y = theta = excursion angle in radians
> > A = I = moment of inertia = 13,138,117.34 g cm^2
> > B = R = damping = for now I assume this to be zero
> > C = k = torsion constant  = 724.68 g cm^2 sec^-2
> > d = moment arm = 93.09 cm
> > D = 2GMmd = 2 * 6.67*10^-8 * 158100 * 729.8 * 93.09 = 1432.82
> > a = distance between weights = 22.10 cm
>
> I would truly appreciate help with this. Thanks

Hello

With your data and units you can use

sol=DSolve[{13.138 10^6 y''[t]+724.68
y[t]==1432.82/22.10^2,y'[0]==0,y[0]==0},y[t],t];
Plot[sol[[1,1,2]],{t,0,3000}]

I hope this helps.

Best Regards
Norbert Marxer