The height of a spring loaded pen

[jamesd2008]

Hi, you no those pens, that you have to push the top down, which is loaded with a spring to use? Well I was wondering if I released it on my desk how high would the pen travel?

I know that the spring PE=0.5kx^2 and the the spring force is F=Kx, but not sure were to go from there?

Thanks James

 

[jack action]

Energy conservation:

½*k*x² = m*g*h

where m is mass of the pen.