The distance travelled in the Y-axis by an arrow

[sandercock]

hi

I am normally good at physics, but i am abit stuck, because i feel I am missing relevant information.

A 100g arrow is shot vertically from a bow whose effective spring constant is 500 n/m,If the bow is drawn 65cm before shooting the arrow, to what height does the arrow rise?

i worked out the force being put on the arrow is 325 N, but how do i work out the initial velocity?i know that when i have that i can just do the equation

Y=VoSin0ot-0.5gt^2
etc to find the distance in the Y-axis, but how do i get to this step!

Help me!

/alex

 

[Stonebridge]

Why not use energy considerations?
There is potential energy stored in the bow; what happens to it?