A particle of mass m and charge q is thrown from origin at t=0 with velocity $2\stackrel{\wedge }{i}+3\stackrel{\wedge }{j}+4\stackrel{\wedge }{k}$ units in a region with uniform magnetic field $\overrightarrow{B}=2\stackrel{\wedge }{i}$ units. After time $t=\pi m/qB$, an electric field $\overrightarrow{E}$ is switched on such that particle moves on a straight line with constant speed. $\overrightarrow{E}$ may be;