What is the required force to push a box upwards on an angled surface?

[Waelroe]

Homework Statement

A box is placed on an angeled surface.

m = 15 kg
f = 0,3

[PLAIN]http://img5.imageshack.us/img5/8717/friction.png

Will the box slip downwards if X = 0?

How big does the force X have to be to push th box upwards?

Homework Equations

The Attempt at a Solution

My idea was that the only force working upwards is Ff.

A = 55°
g = 9,81
N = mg*cos(90-35)+18 = 102,40 N

Ff = 0,3*N = 30,72

Force downwards: mgcos35-18 = 102,54 N

The force down is greater than Ff therefore it would slip if X = 0.To get how big X needs to be to make the box move up i simply subtracted the force down with Ff and got = 71,82 N.Could this possibly be correct?

 

[Pi-Bond]

Why is your downward force mgcos(35)-18? It should just be mgcos(35)

 

[Waelroe]

Why is your downward force mgcos(35)-18? It should just be mgcos(35)

Yea, okey. So the rest would be correct then?

 

[Pi-Bond]

After changing the value of the downward force, yes.