An alpha particle $($m $=6\mathrm{.}64$x$10-27$ kg q $=3\mathrm{.}2$x$10-19$ C$)$ is fired at a proton. If the alpha particle is moving at a velocity of $3\mathrm{.}0$x$106$ m$/$s $[$W$]$ and the proton is moving with a velocity of $5\mathrm{.}5$x$106$ m$/$s$[$E$]$ determine the distance of closest approach between the two particles. You may assume that the particles are far apart to start.