Energy - Finding Spring Constant

[njanek]

Homework Statement

If a mass (.5 lb) is pushed down a ramp at a constant unknown force into a spring, compressing it 3 inches, what is the spring constant?

Homework Equations

Mass: .5lb
Time: 3 seconds
Length of ramp: 28 inches
inital height of ramp: 5.5 inches
final height: 0
µ: .52
The ramp angle is 15^o to the ground

The Attempt at a Solution

I understand that if I set the equation up like this:

1/2mv²_o + mgh_o + 1/2Kx²_o + Wnc = 1/2mv² + mgh + 1/2Kx²

And plug in what I know, I will find the answer for the spring constant, But I'm having trouble finding the work of the non conservative forces. and the final and initial velocities. I just need help figuring them out so I can solve for K.

Thank you to anyone who helps :) I really appreciate it!

 

[Delphi51]

If the unknown force is large, it will give the mass a lot of energy and the spring will have to be very strong. Or if the force is very small, the spring will be very weak.
The strength of the spring depends on the force and cannot be found without knowing the force. Or something else not given in the question.