Describe how the strong nuclear force between two nucleons varies with their separation distance, $r$.

Name the stable hadron found in a hydrogen-1 nucleus and state its quark composition.

Write a decay equation in terms of the quark model for beta-plus (${\beta }^{+}$) decay.

The radius of a nucleus is given by $R=r_0{A}^{1/3}$ where $r_0$ is a constant and $A$ is the nucleon number. Assuming the average mass of a single nuclear is $m$, show that the mean density $\rho$ of a nucleus is independent of its nucleon number $A$, and express $\rho$ in terms of $m$ and $r_0$.