If the velocity of the incident charged particle were doubled, how would b have to change (keeping all other parameters constant to keep the trajectory of the particle the same?

A1-lb collar is attached to a spring and slides without friction along a circular rod in a vertical plane. the spring has an undeformed length of 5 in. and a constant k =25 lb/ft. knowing that the collar is released from being held at a determine, the speed of the collar and the normal force between the collar and the rod as the collar passes through b.