In the region between the plane `z=0` and `z=a (a gt 0)`, the uniform electric and magnetic fields are given by `vecE=E_(0)(hatk-hatj)`, `vecB=B_(0)hati`. The region defined by `a le z le b` contains only magnetic field `vecB= -B_(0)hati`. Beyond `z gt b` no field exits. A positive point charge `q` is projected from the origin with velocity `v_(0)hatk`. Assuming the mass of the particle to be `(2)/(3)(qE_(0)a)/(v_(0)^(2))`.
When the particle just reverse its direction, all the fields are switched off. Time taken by the particle to touch the plane `z=0` from that instant is

Options

A. `a//v_(0)`
B. `a//2v_(0)`
C. `(a)/(3v_(0))`
D. `(a)/(4v_(0))`

Explanation

After the field are switched off, velocity remains constant