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

AI Thread Summary
A 250-N horizontal force is applied to push a 29-kg box up an inclined plane at constant speed, prompting a calculation of the normal force (FN) and coefficient of kinetic friction (µk). Initial calculations for FN did not consider the incline angle, leading to incorrect results. The discussion emphasizes the importance of analyzing forces in both vertical and horizontal directions to derive the correct equations. Participants suggest reevaluating the approach by accounting for all forces acting on the box, including gravitational and frictional forces. Accurate determination of FN and µk requires a comprehensive understanding of the forces involved on the incline.
gcombina
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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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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.
 
ok FN = Mg
= 250N sin 27
= 113

still not the right answer
 
squelch said:
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.
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.)
 
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