Problem 3.401

A particle with specific charge $q / m$ is located inside a round solenoid at a distance $r$ from its axis. With the current switched into the winding, the magnetic induction of the field generated by the solenoid amounts to $\bar{B}$. Find the velocity of the particle and the curvature radius of its trajectory, assuming that during the increase of current flowing in the solenoid the particle shifts by a negligible distance.