# Question:Problem with ODE system

## Question:Problem with ODE system

Maple

I'm trying to solve a system of two differential equations of the second order in Maple. I set it up as a system of four differential equations of the first order, but after calling for the solution, all I get back is what I entered in without receiving a solution of any sort. What do I need to fix?

Here's what I did:

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> with(plots);
print(`output redirected...`); # input placeholder

> m := 0.46e-1; d := 0.42e-1; v := 60; alpha0 := 12; g := 9.81; pa := 1.205; cd := .2; n := 100; omega := 2*Pi*(1/60);

> p := 6*m/(Pi*d^3);

> k1 := (3/4)*cd*pa/(d*p); k2 := (3/8)*omega*pa/p;

> gl1 := vx(t) = diff(x(t), t);
> gl2 := vy(t) = diff(y(t), t);

> gl3 := diff(vx(t), t) = -k1*vx(t)*(vx(t)^2+vy(t)^2)^(1/2)-k2*vy(t);

> gl4 := diff(vy(t), t) = -g-k1*vy(t)*(vx(t)^2+vy(t)^2)^(1/2)+k2*vy(t);

> init1 := x(0) = 0;
> init2 := y(0) = 0;
> init3 := vx(0) = v*cos((1/15)*Pi);
> init4 := vy(0) = v*sin((1/15)*Pi);

> sol; dsolve({gl1, gl2, gl3, gl4, init1, init2, init3, init4}, {vx(t), vy(t), x(t), y(t)}, type = numeric);

> sol(.1);
sol(0.1)

> odeplot(sol, t, x(t), t, y(t), t = 0 .. 1);
Error, (in plots/odeplot) input is not a valid dsolve/numeric solution

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After calling for the solution at t=0.1, I don't get anything back. I also tried plotting the solution, but then I receive an error message.

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