Chapter 4.4, Problem 5P

(a) A mass weighing $2$ lb stretches a spring $6$ in. If the mass is pulled down an additional $3$ in. and then released, and if there is no damping, determine the position $y$ of the mass at any time $t$. Plot $y$ versus $t$. Find the frequency, period, and amplitude of the motion.

(b) Draw a phase portrait of the equivalent dynamical system that includes the trajectory corresponding to the initial value problem in part (a).