A charge q moving along the X-axis with a velocity v

A charge q moving along the X-axis with a velocity v is subjected to a uniform magnetic field B acting along the X-axis as it crosses the origin O.
(i)Trace trajectory.
(ii) Does the charged particle gain kinetic energy as it enters the magnetic field? Justify your answer.

(i) As, the charged particle is moving perpendicularly to the magnetic field. So, it will perform circular motion in XY-plane.
(ii) No, the charged particle does not gain any KE as Lorentz force acting on it does not perform any work as { F }_{ m } perpendicular to v.