Answer
$t = 3.6 \times 10^{-22} s$
Work Step by Step
From the classical kinetic energy formula,
$t = \frac{d}{v} = \frac{d}{\sqrt {2k/m}} = 2r \sqrt {\frac{m_n}{2k}} = \frac{r}{c} \sqrt \frac{{2mc^2}}{K}$
$t = \frac{(1.2 \times 10^{-15} m) (100^{1/3})}{3.0 \times 10^8 m/s} \sqrt \frac{{2(939.6 MeV)}}{5MeV}$
$t = 3.6 \times 10^{-22} s$
