Motion of mass hanging from a spring is modeled y''=-π^2y

Given Y(0)=5 and y(3/2)=8, find:

The particular solution of this IVP and the first time (t is positive) at which the velocity is zero.

I believe i've found the IVP and that it's y(t)=12.124sin(πt)+5cos(πt) .I'm not sure if it's correct though, but I don't know how to find the velocity. Thanks!