Elastic Potential Energy- finding spring constant

[bigboss]

Homework Statement

In a physics lab experiment, a spring clamped to the table shoots a 22 g ball horizontally. When the spring is compressed 18 cm, the ball travels horizontally 5.2 m and lands on the floor 1.5 m below the point at which it left the spring.

Homework Equations

Us= .5kx^2

The Attempt at a Solution

I tried to find the elastic potential energy and then i got stuck.

 

[Cyosis]

Use energy conservation. When the spring is compressed the ball is stationary so all its energy is elastic potential energy. When the spring is released the ball loses potential energy and gains kinetic energy.

 

[bigboss]

how would i find the velocity?

 

[Cyosis]

With $y=y_0+v_{0,y}t-\frac{1}{2}gt^2$ and $x=v_{0,x} t$.