In a certain region, uniform electric field `E=-E_0hatk` and magnetic field `B = B_0hatk` are present. At time `t = 0`, a particle of mass m and charge q is given a velocity `v = v j + v k`. Find the minimum speed of the particle and the time when it happens so.

Explanation

`a_e=(qE_0)/m` (along negative z-direction)
Electric fiedl will make z - component of velocity zero. At that time speed of the particle will be minimum and that minimum, speed ils the other component i.e. `v_0`.
`v_z=u_z+a_zt`
`or 0=v_0 -(qE_0)/mt`
`or t=(mv_0)/(qE_0)`