Date: Dec 6, 2012 4:56 AM
Author: hazem.abdelhafiz@gmail.com
Subject: System of differential equations

Dear all,
I want to solve this system of equations but I always get an error

NDSolve::ndnum:Encountered non-numerical value for a derivative at t==0

can any one help me on this

s=NDSolve[{
ph1''[t]+ph1'[t]+sin[ph1[t]]-mu[t]-mu'[t]==0.005,
ph2''[t]+ph2'[t]+sin[ph2[t]]+mu[t]+mu'[t]==0.005,
0.2mu'[t]+mu[t]==ph1'[t]-ph2'[t],
ph2[0]==0,
ph1[0]==0,
ph2'[0]==0,
ph1'[0]==0,
mu[0]==0
},
{ph1[t],ph2[t],mu[t]},
{t,0,5000}
]

thanks in advance,