\documentclass[tikz]{standalone}\input{pre.tex}\begin{document}\begin{tikzpicture}
\def\angle{50}
% \draw (0,2) coordinate (o) circle (2);
% \draw (o) circle (0.5);
% \draw (0,0) -- (5,6);
\draw[interface] (0,6.25) rectangle (6,6);
\draw[thick] (0,6) --(2.85,6) (3.15,6) --(6,6);
\draw[interface] (0,6.25) rectangle (6,6);
\draw [interface, draw=black]
(2.85,6) rectangle (3.15,4);
\def\rr{0.8}
% \draw[axis] (1.2,-3.15) --(1.20,4);
\draw[axis, ->] (0,4) -- ++(0,-4) node[below] {$x$};
% \draw[axis] (3,4) ++ (1.8,0) arc (0:180:1.8);
\draw[fill=white] (3,4) circle (\rr);
\path (3,4) -- +(-\rr,0) coordinate (Cl) + (\rr,0) coordinate (Cr);
\draw[fill=black] (3,4) circle (3pt);
\draw[black!70] (Cr) -- ++ (0,-3) coordinate (B);
\draw[black!70] (Cl) -- ++ (0,-3) coordinate (2m);
\draw[force, ->] (2m) -- ++(0,1) node[left] {$\vec{T}_1$};
\draw[force, ->] (Cl) -- ++(0,-1) node[left] {$\vec{T}'_1$};
\draw[force, ->] (Cr) -- ++(0,-1) node[right] {$\vec{T}'_B$};
\draw[force, ->] (B) -- ++(0,1) node[right] {$\vec{T}_B$};
\draw[force,->] (2m)-- node[left] {$\vec{u}$} ++(0,0.5);
\draw[] (B) circle (\rr) node[right] {$B$};
\path (B) -- +(-\rr,0) coordinate (Bl) + (\rr,0) coordinate (Br);
\draw[fill=black] (B) circle (3pt);
\draw[fill=black] (2m) rectangle ++(0.2,-0.6) rectangle ++(-0.4,0.6) node[left] {$2m$};
\draw[force, ->] (Br) -- ++(0,-0.7) node[right] {$\vec{T}'_3$};
\draw[force, ->] (Bl) -- ++(0,-0.7) node[left] {$\vec{T}'_2$};
\draw[black!70] (Br) -- ++ (0,-3) coordinate (o);
\draw[black!70] (Bl) -- ++ (0,-2) coordinate (m);
\draw[force,->] (m)-- node[anchor=north east] {$\vec{u}$} ++(0,-1.5);
\draw[force, ->] (m) -- ++(0,0.5) node[left] {$\vec{T}_2$};
\draw[force, ->] (o)++(0,0.5) -- ++(0,0.5) node[right] {$\vec{T}_3$};
\draw[fill=black] (m) rectangle ++(0.1,-0.6) rectangle ++(-0.2,0.6) node[left] {$m$};
\draw[force,->] ($(o)-(0.2,0)$)--node[left] {$\vec{v}$} ($(o)-(0.2,-1.2)$);
\node[inner sep=0pt, scale=0.2, xshift=-2em] (russell) at (o)
{\includegraphics[width=.25\textwidth]{img/monkey.png}};
\node[right, xshift=1em] at (o) {$m$};
% \draw[force,->] ($(o)-(0.7,1.2)$)--node[left] {$\vec{v}$} ($(o)-(0.7,-1.2)$);
\end{tikzpicture}\end{document}
