# draw a little 3d graphic with tikz

I would like to draw a little 3D Graphic with TikZ.

I dont know how to draw these lines on the left site...

Now, i try something like that:

\documentclass[12pt,a4paper]{scrartcl}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\draw (0,0)--(4,0)--(4,-1.5)--(2.5,-2.8)--(-0.5,-2.8);
\draw (4,0)--(2.5,-1)--(-0.5,-1);
\draw (2.5,-1)--(2.5,-2.8);
\end{tikzpicture}
\end{document}


Thank you all.

Your diagram is not very clear, especially the arrows. So I leave the arrow to you. An arrow in the middle of a line can be drawn as in TikZ: How to draw an arrow in the middle of the line?.

If you want the arrows to have an "over each other" effect, you may borrow preaction:

\documentclass[tikz]{standalone}
\tikzset{
my line/.style={preaction={draw=white,line width=#1},-latex},
my line/.default=3pt
}
\begin{document}
\begin{tikzpicture}
\draw (2,0) -- (6,0) -- (6,-3) -- (4,-5) -- (4,-2) -- (6,0)
(0,-2) -- (4,-2) (0,-5) -- (4,-5);
\draw[my line] (5,-5) -- (5,1);
\draw[my line] (5,-2.5) -- (9,-2.5);
\draw[my line=5pt,very thick] (7,-.5) -- (2,-5.5)
node[pos=0.8,above left] {$M_b$};
\end{tikzpicture}
\end{document}