Finding the coefficient of Kinetic force with an angle

[KellyTarzuoty]

Homework Statement

A 1000N crate is being pushes across a level floor at a constant speed by a force (F) of 300N at an angle of 20 degrees below the horizontal, what is the coefficient of kinetic force?

Homework Equations

Fk= uk*N
uk= Fk/N[/B]
Fk=F2

The Attempt at a Solution

in the back of the textbook it comes up as 0.256, but when I try I do:
Fk = F2
F2 = 300cos20 = 281.9
uk= F2/n
uk= 281.9/1000
uk= 0.281

Can someone tell me where I've gone wrong? It seemed like it should be a simple question

 

[Nathanael]

The normal force from the ground is not always the weight of the object.
The normal force is what ever it needs to be to keep the block from accelerating vertically.

 

[KellyTarzuoty]

The normal force from the ground is not always the weight of the object.
The normal force is what ever it needs to be to keep the block from accelerating vertically.

okay, so should I try and use that to try and find the weight? Because that was all the question gave me, it didn't mention any weights.

 

[Nathanael]

okay, so should I try and use that to try and find the weight? Because that was all the question gave me, it didn't mention any weights.

The weight of the crate is given, it is 1000N.
In your equations you seem to be saying that the normal force is equal to the weight of the crate (1000N).

If I push down on a piece of paper, the normal force on the paper (from the table or whatever) is going to be much more than the weight of the paper, right?

 

[haruspex]

The normal force from the ground is not always the weight of the object.
The normal force is what ever it needs to be to keep the block from accelerating vertically.

To be precise and general, the normal force from a surface is the force of least magnitude required to prevent the object penetrating the surface. Necessarily, that will be at right angles to the surface.

@KellyTarzuoty, draw a free body diagram of the block. Three forces act on it. What are they? Use the usual statics equations to find the normal force.