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.