Finding kinetic friction force and coefficient on an inclined plane

[nukeman]

Homework Statement

Im working on some typical "Ramp being pulled up an incline" questions and have trouble understanding something.

An example question where it stats a box is being pulled up a ramp like the image below:

Image: http://i43.tinypic.com/jb486q.jpg

Now, first: In order to find the friction force exerted on the box.

Would I simply just apply this: Δk - ΔUgravity / distance ?

AND...To find the coefficient of Kinetic friction, do I just go:

First find the normal force? which would be: n -mg cos 30 = 0, solve for n, which is 42.2N

THEN, just use this formula? ; fk = µk n ?

Homework Equations

The Attempt at a Solution

 

[Delphi51]

Isn't n = mg cos(30) ?
Yes, Ff = µk*n and Ff = Δk - ΔUgravity / distance