Calculating Eraser's Distance on Friction Desk

[Matt1234]

Homework Statement

A student uses a compressed spring of force constant 22 N/m to shoot 0.0075 kg eraser across a desk. The magnitude of the force of friction on the eraser is 0.042N. How far along the horizontal desk will the eraser slideif the spring is initially compressed 3.5 cm? Use the law of conservation of energy.

Homework Equations

Ee = .5 K x^2
Ek = 0.5 m v^2
w = f d cos ()

The Attempt at a Solution

http://img189.imageshack.us/i/lastscank.jpg/

 

[bucher]

You don't need the kinetic energy equation for this problem. Set the spring energy equal to the friction energy and solve for the unknown d that the eraser would have to travel to make the equality true.