14. A 7 Kg box sits on an incline of 30°, what is the force down the incline?

To know the force down you need to divide the force into two components X parallel with the inclined surface and Y, the perpendicular one.

F = m * g = 7kg*9,8m/s^2 = 68.6 N

Fy = F*cos (30) = - N

Fx = F*sen (30)

N = normal. Force which is perpendicular to the movement equal and opposite to weigh in the plane.

Friction force = Fr = Coef * N

In the inclined there're Fx to one side and Fr to the other side. Perpendicular to it there are Fy and N