There is region of space where uniform magnetic field of induction B exists. The field exists at all points for which `x-` coordingates are positive. The direction of field ia along negative z axis.
Now a certain charged particle of mass m and charge q a certain speed enters in this region. A magnetic field at a point whose coordinates are `x=0,y=-d` and `z=0` . Magnetic force will start acting on the particle and particle moves in a uniform circular motion, such that origin becomes centre of circular path described by it
The speed of the charge particle will be

Options

A. particle will come out from the region of uniform magnetic field at a point `(a=0,y=d,z=0)` with speed `(2qBd)/(m)`
B. particle does not remain always in the `x-y` plane
C. The `x-`coordinate of location of particle will be d at a time `t=(pi m)/(qB)`
D. particle will emerge out of the region of field after a time `(pi m)/(qB)` with speed `(qBd)/(m)`

Answer

D

Explanation

`theta=omegat, omega=(qB)/(m),pi=(qB)/(m).timpliest=(pim)/(qB)`