Normal force (dynamic)?

Question

I feel really stupid right now as I have answered hundreds of questions like this, but never in in inequilibrium. Box on incline: what is the magnitude of the normal force on a box on an incline plane, no friction, not static (it is sliding down)

Chances are I will have it figured out shortly but even I have huge brain farts

Answer 1

if the angle of incline is A, then the normal force is Force of gravity times cosine(A).

to explain: draw a diagram, including force of gravity, and the normal force (always directly out of the surface) and turn the paper so that the inclined surface is now horizontal and the gravity is not. Split the gravity into components, then the vertical component must be equal to the normal force ('cause the box is not falling into the plane) and the horizontal component of the gravity is pulling it down the plane.