$3/158$ The collar has a mass of $2$ kg and is attached to the light spring, which has a stiffness of $30\frac{N}{m}$ and an unstretched length of $1\mathrm{.}5$ m $.$ The collar is released from rest at A and slides up the smooth rod under the action of the constant $50-N$ force. Calculate the velocity $v$ of the collar as it passes position $B.$