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Homework Statement:
 Suppose the force exerted by a spring is F(x) = kx and the spring has constant k = 325 N/m. Then suppose a wooden cube headed east with mass m = 6 kg traveling with an initial velocity on a level surface with kinetic coefficient of friction 0.250 presses against the spring and it compresses from x = 0 to x = 0.70 meters as it stops. What is the net work done? HINT: You need to integrate to solve.
Relevant Equations:

F(x) = kx and the spring has constant k = 325 N/m
Kinetic coefficient of friction 0.250
Spring compresses from x = 0 to x = 0.70 meters
W_net = Integral from 0 to 0.70 meters [  F_spring  F_friction ]
= 1/2 * (k) * x^2  mu * mg * normal force * x
= 1/2 * (325N/m) * (.70)^2  0.250 * 6kg * 9.81m/s^2 * 0.70  0
=  89.93 Joules
Is this correct and am I setting this whole thing up correctly? The negative signs have me bit confused. Also, am I supposed to integrate the Force of friction like this or do I treat it as a constant?
Thanks for the help
= 1/2 * (k) * x^2  mu * mg * normal force * x
= 1/2 * (325N/m) * (.70)^2  0.250 * 6kg * 9.81m/s^2 * 0.70  0
=  89.93 Joules
Is this correct and am I setting this whole thing up correctly? The negative signs have me bit confused. Also, am I supposed to integrate the Force of friction like this or do I treat it as a constant?
Thanks for the help