\documentclass[tikz]{standalone}\input{pre.tex}\begin{document}\begin{tikzpicture}[
force/.style={>=latex,draw=blue,fill=blue},
% axis/.style={densely dashed,gray,font=\small},
axis/.style={densely dashed,black!60,font=\small},
interface/.style={
pattern = north east lines,
draw = none,
pattern color=gray!60,
},
cargo/.style={
rectangle,
fill=magenta!40,
draw=black!50,
inner sep=2.5mm,
},
spring/.style={
decoration={
aspect=0.3,
segment length=.8mm,
amplitude=2mm,
coil},
decorate,
draw=magenta!25
},
interface1/.style={draw=gray!60,
% The border decoration is a path replacing decorator.
% For the interface style we want to draw the original path.
% The postaction option is therefore used to ensure that the
% border decoration is drawn *after* the original path.
postaction={draw=gray!60,decorate,decoration={border,angle=-135,
amplitude=0.3cm,segment length=2mm}}},
scale=0.75
]
\def\angle{41}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\draw[force,->] (-3,-3) -- ++(1,0) node[right]{$\vec{v}_0$};
\contourlength{1mm};
\draw[thick] (0,0) -- ++(0,-3);
\draw[thick,->] (0,0) -- node[right] {$\vec{l}$} ++(0,-2.65);
\draw[thick,->] (0,0) -- node[right, above] {$\vec{r}$} ++(-2.8,-2.69);
\draw[interface] (-3,0) rectangle ++(6,0.5);
\draw[line width=0.4mm] (-3,0) -- ++(6,0);
\draw[fill=magenta] (0,0) circle (3pt) node[above, yshift=3pt] {\contour{white}{$O$}};
\draw[fill=magenta] (0,-3) circle (0.35) node {\contour{white}{$m$}};
\draw[fill=magenta] (-3,-3) circle (0.35) node {\contour{white}{$m$}};
\draw[axis,->] (-3,-4) -- ++(6,0) node[right] {$+x$};
\draw[force,->] (0,0) -- (-1,0) node[left, below]{$\vec{f}$};
\end{tikzpicture}\end{document}
