A proton and an α -particle, having kinetic energies K_p and K_α respectively, enter into a magnetic field at right angles. The ratio of the radii of…

A proton and an $\displaystyle \alpha$-particle, having kinetic energies $\displaystyle \mathrm{K}_{\mathrm{p}}$ and $\displaystyle \mathrm{K}_\alpha$ respectively, enter into a magnetic field at right angles. The ratio of the radii of trajectory of proton to that of $\displaystyle \alpha$-particle is $\displaystyle 2$ : 1. The ratio of $\displaystyle \mathrm{K}_{\mathrm{p}}: \mathrm{K}_\alpha$ is :