# Normal Force and Coefficient of kinetic friction (Quiz 4, q15)

1. Aug 30, 2014

### gcombina

A 250-N force is directed horizontally as shown to push a 29-kg box up an inclined plane at a constant speed. Determine the magnitude of the normal force, FN, and the coefficient of kinetic friction, µk.
FN µk
(a) 330 N 0.31
(b) 310 N 0.33
(c) 250 N 0.27
(d) 290 N 0.30
(e) 370 N 0.26

My attempt:

I know FN = mg
so FN = (29kg) (9.8 m/s^2)
FN = 284

why is it not right?

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2. Aug 30, 2014

### squelch

From the diagram and equations you've provided, it doesn't appear that you've accounted for the angle of the incline. Try to account for that.

3. Aug 30, 2014

### gcombina

ok FN = Mg
= 250N sin 27
= 113

4. Aug 30, 2014

### haruspex

That's not the only omission.
gcombina, choose two directions, e.g. vertical and horizontal. In each direction, list all the forces that act in that direction. What two equations can you write?
(if you prefer, you can choose parallel to the plane and normal to the plane, or horizontal and normal to the plane, whatever.)