Assertion (A): An electron and a proton enter with the same momentum $\overrightarrow{\mathit{p}}$ in a magnetic field $\overrightarrow{\mathit{B}}$ such that $\overrightarrow{\mathit{p}}\mathit{⟂}\overrightarrow{\mathit{B}}$. Then both describe a circular path of the same radius.
Reason (R): The radius of the circular path described by the charged particle (charge q, mass m) moving in the magnetic field $\overrightarrow{\mathit{B}}$ is given by $\mathit{r}=\frac{\mathit{m}\mathit{v}}{\mathit{q}\mathit{B}}$.