\documentclass{article}
\usepackage[a4paper,margin=2cm]{geometry}
\usepackage[latin1]{inputenc}
\usepackage{pstricks-add,pst-eqdf,pst-func}
\usepackage{array,amsmath}

%%%%%%%%%%%%%%%%%%
\def\datRoot{C:/Users/J\"{u}rgen/Desktop/gravitation/}

\begin{document}

\def\eqlancerA{%
y[2]|y[3]|-d0/m0*y[2]|-d0/m0*y[3]-g0}%
\def\eqlancerB{%
y[2]|y[3]|0|-g0}%

\section{Un lancer inclin\'{e} avec du frottement}

Les \'{e}quations diff\'{e}rentielles sont :
\begin{align*}
\ddot{x}&=-\frac{d}{m}\dot{x}\\
\ddot{y}&=-\frac{d}{m}\dot{y}-g
\end{align*}

\begin{center}
\begin{pspicture}(-0.5,-0.5)(10,6)
\pstVerb{
    /m0 1 def
    /d0 0.75 def
    /theta0 60 def
    /x0 0 def
    /y0 1 def
    /v0 10 def
    /v0x v0 theta0 cos mul def
    /v0y v0 theta0 sin mul def
    /g0 9.81 def 
}%
\psaxes[labels=none,ticks=none]{->}(0,0)(0,0)(10,5)
\uput[0](10,0){$x$}
\uput[90](0,5){$y$}
\rput(!0 y0){%
\psline[linecolor=gray]{->}(0;0)(!2 theta0 cos mul 2 theta0 sin mul)
\psline[linestyle=dashed](0,0)(1.5,0)
\psarc{->}(0,0){1}{0}{!theta0}
\rput(!2.2 theta0 cos mul 2.2 theta0 sin mul){$\vec{v}_0$}
\rput(!0.5 theta0 2 div cos mul 0.5 theta0 2 div sin mul){$\alpha$}
}
\psequadiff[method=rk4,
            plotpoints=1000,
            algebraic,
            whichabs=0,
            whichord=1,
            tabname=XiAYiA
%           ,saveData,filename=XiYi.dat
]{0}{5}{x0 y0 v0x v0y}{\eqlancerA}%
\listplot[linecolor=blue]{XiAYiA aload pop}
\psequadiff[method=rk4,
            plotpoints=1000,
            algebraic,
            whichabs=0,
            whichord=1,
            tabname=XiBYiB
%           ,saveData,filename=XiYi.dat
]{0}{5}{x0 y0 v0x v0y}{\eqlancerB}%
\listplot[linecolor=red]{XiBYiB aload pop}

\end{pspicture}
\end{center}



\end{document}
