How Do You Calculate the Coefficient of Friction in a Spring Problem?

[synergix]

Homework Statement

Question 6

http://web.viu.ca/hearnd/Courses/Phys121/F02Test2/Page3.htm"

Homework Equations

(E_ps+E_K)_i-F_fr= (E_ps+E_k)_f

The Attempt at a Solution

both kinetics should be zero so..

1/2(50Nm)(0.10m)²+0-(0.50kg)(9.81m/s²)u_k= 1/2(50Nm)(-0.08m)²+0

u_k= (0.25-0.16)/(0.5kg)(9.81m/s²)

this must be wrong the posted answer is different then this would yield. This seems like a very straightforward question what am I missing?

Thanks

 

[synergix]

figured it out...
Force of friction x distance in an energy equation duh.