Adding a proton to a nucleus The nucleus of an atom is positively charged because it consists of positively charged protons and uncharged neutrons. To bring a free proton toward a nucleus, a repulsive force $F(r)=k q Q / r^{2}$ must be overcome, where $q=1.6 \times 10^{-19} \mathrm{C}$ is the charge on the proton, $k=9 \times 10^{9} \mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{C}^{2}, Q$ is the charge on the nucleus, and$r$ is the distance between the center of the nucleus and the proton. Find the work required to bring a free proton (assumed to be a point mass) from a large distance $(r \rightarrow \infty)$ to the edge of a nucleus that has a charge $Q=50 q$ and a radius of $6 \times 10^{-11} \mathrm{m}$