Electromagnetic Waves

The electric fields of two plane electromagnetic plane waves in vacuum are given by $\overrightarrow {{E_1}} = {E_0}\widehat j\cos \left( {\omega t - kx} \right)$ and $\overrightarrow {{E_2}} = {E_0}\widehat k\cos \left( {\omega t - ky} \right)$ At t = 0, a particle of charge q is at origin with a velocity $\overrightarrow v = 0.8c\widehat j$ (c is the speed of light in vacuum). The instantaneous force experienced by the particle is :