Two rectangular plates A and B placed at a distance 2a apart, are connected to a battery to produce an electric field. There are insulators between plates C and other two plates. A magnetic field exists along z-axis. A charged particle of mass m and charge q passes through a hole at the middle of the plate A with velocity v and strikes at Q which is the middle of the bottom edge of plate B after passing through a hole in plate C. If E=m v^{2} / q a what will be the speed of the particle at Q?