In a certain region of space, there exists a uniform and constant electric field of magnitude E along the positive y-axis of a coordinate system. A charged particle of mass m and charge -q (qgt0) is projected form the origin with speed 2v at an angle of 60^@ with the positive x-axis in x-y plane. When the x-coordinate of particle becomes sqrt3mv^2//qE a uniform and constant magnetic. field of strength B is also switched on along positive y-axis. z-coordinate of the particle as a function of time after the magnetic field is switched on is