In a certain region of space, there exists a uniform and constant electric field of strength E along x-axis and uniform constant magnetic field of induction B along z-axis. A charged particle having charge q and mass m is projected with speed v parallel to x-axis from a point (a, b, 0). When the particle reaches a point 2a, b/2, 0 its speed becomes 2v. Find the value of electric field strength in terms of m, v and co-ordinates.