Is this solvable using Mathematica?

*To*: mathgroup at smc.vnet.net*Subject*: [mg99048] Is this solvable using Mathematica?*From*: johnboy98105 at yahoo.com*Date*: Sat, 25 Apr 2009 04:50:02 -0400 (EDT)

Supposed you want to define a second order derivative along with your ODEs. (So you can scale the second order term) Example shown below. k1 = 1; r1 = 1; NDSolve[{a'[t] == k1 b[t] - d, a''[t] == r1 b'[t], a'[0] == 0, a[0] == 1, b[0] == 0}, {a[t], b[t]}, {t, 1, 10} ] But I get an error. NDSolve::ntdvmm: Cannot solve to find an explicit formula for the derivatives. NDSolve will try solving the system using a mass matrix method. NDSolve::ndnum: Encountered non-numerical value for a derivative at t == 0.`. Maybe this is more of a math question than software. But I would be very interested in seeing if it's doable in Mathematica. Thanks in advance.