The rest energy of the electron is $m_e c^2$ . So, the total energy is $E = 4 m_e c^2$ . Therefore,
$\begin{align*}E^2 = p^2 c^2 + m_e^2 c^4\end{align*}$
can be solved for $p$ :
$\begin{align*}p = \boxed{m_e c\sqrt{15}}\end{align*}$
Therefore, answer (C) is correct.

Solution to 2008 Problem 22