How Does Friction Affect the Motion of a Block Colliding with a Spring?

[_mae]

Homework Statement

A 1.00 kg object slides to the right on a surface having a coefficient of kinetic friction 0.250. The object has an initial velocity of 3.40 m/s when it makes contact with a light spring that has a force constant of 50.0 N/m. The object comes to rest after the spring has been compressed a distance d. The object is then forced toward the left by the spring and continues to move in that direction beyond the spring's unstretched position. The object finally comes to rest a distance D to the left of the unstretched spring.

http://img221.imageshack.us/img221/4141/p862af4.gif​

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(a) Find the speed v at the unstretched position when the object is moving to the left.
(b) Find the distance D where the object comes to rest.

Homework Equations

(a): E = (1/2)mv^2 = (1/2)mv_{i}^2

The Attempt at a Solution

(a) When I rearrange the equation I gave above, (1/2)mv^2 = - (1/2)mv_{i}^2. This eventually gives the relationship v^2 = -v_{i}^2. If the initial velocity is 3.40 m/s, then wouldn't the velocity towards the left after the collision be -3.40 m/s? I typed this in, but I guess it's wrong.

(b) I don't know what to do here :(

 

[_mae]

I still need help... :(

 

[Mindscrape]

If we were dealing with conservative forces you would be absolutely correct, but friction is a nonconservative force.