Speed of a ball launched from a spring

[cilantrone]

Homework Statement

The force required to compress an imperfect horizontal spring an amount x is given by F = 150x + 12x^3, where x is in meters and F in Newtons.
If the spring is compressed 2.5m, what speed will it give to a 3.5kg ball held against it and then released?

Homework Equations

Not sure all these are relevant, but...
F = ma
a = dv/dt
K = mv^2 /2

The Attempt at a Solution

I made many attempts and the computer told me that none were right.

Thanks!

 

[Hootenanny]

Homework Statement

The force required to compress an imperfect horizontal spring an amount x is given by F = 150x + 12x^3, where x is in meters and F in Newtons.
If the spring is compressed 2.5m, what speed will it give to a 3.5kg ball held against it and then released?

Homework Equations

Not sure all these are relevant, but...
F = ma
a = dv/dt
K = mv^2 /2

The Attempt at a Solution

I made many attempts and the computer told me that none were right.

Thanks!

Welcome to PF cilantrone,

Just looking at the relevant equations that you have listed, I notice that there is a vital one missing, the definition of work.