1.If a mass-spring system is underdamped and modeled with the IVP

x"+x'+x=0, x(0)=1, x'(0)=1

then the solution of the ODE predicts that the mass will pass through the equilibrium positioninfinitely many times

2.If x(t)= -cos(pi*t)-sin(pi*t) represents the position of a mass on a spring, then the phase is equal to pi/4