The vertical motion of a mass attached to a spring is described by the IVP Solution the associated equation is 1/4x^2+x+1=0 or x^2+4x+4=0 (x+2)^2=0 so the solution is of the form x=Ae^(-2t)+Bte^(-2t) using x(0)=4 we get A=4 x\'(0)=-2A+B=2 B=10 x=4e^(- 2t)+10te^(-2t) x\'=-8e^(-2t)+10e^(-2t)-16te^(-2t)=0 2-16t=0 t=1/8 x\'>0 before 1/8 and x\'>0 after 1/8 So the maximum vertical is when t=1/8.