\begin{problem*}{4}
Two protons in an atomic nucleus are typically seperated by a distance of $r = 2.00\E{-15}\U{m}$.
The electric repulsion force $F$ between the protons is huge, but the attractive nuclear force is even stronger and keeps the nucleus from bursting apart.
What is the magnitude of $F$?
\end{problem*}

\empaddtoprelude{
  pair A, B;
  A := origin;
  B := (3cm, 0);
  def drawB = 
    draw_pcharge(A, 6pt);
    draw_pcharge(B, 6pt);
    label.bot("r", draw_length(A, B, 10pt));
  enddef;
}

\begin{nosolution}
\begin{center}
\begin{empfile}[2ns]
\begin{emp}(0cm, 0cm)
  drawB;
\end{emp}
\end{empfile}
\end{center}
\end{nosolution}

\begin{solution}
\begin{center}
\begin{empfile}[2]
\begin{emp}(0cm, 0cm)
  label.top("F", draw_force(A, B, 20pt));
  drawB;
\end{emp}
\end{empfile}
\end{center}

\begin{equation}
 F = k_e \frac{q^2}{r^2}
   = 8.99\E{9}\U{N$\cdot$m$^2$/C$^2$} \left(\frac{1.60\E{-19}\U{C}}{2.00\E{-15}\U{m}}\right)^2
   = \ans{57.7\U{N}}
\end{equation}
\end{solution}
