Forces in Two Dimensions - Mission F2D5 Detailed Help

An object is placed upon an inclined plane with an incline angle of 25 degrees. As the incline angle is increased towards 90 degrees, the normal force experienced by the object ____.

An object that is in contact with a stable surface experiences a normal force that is always directed perpendicular to the surface. In the case of inclined planes, the normal force is directed perpendicular to the plane. The value of the normal force must be equal to the perpendicular component of gravity (see Math Magic section) so that there is a balance of forces along an axis perpendicular to the plane. Since the perpendicular component of gravity depends on the angle that the incline makes with the horizontal, the normal force must also depend upon the angle. Predicting how a change in the angle would affect the value of the normal force is a mere matter of thinking about the equation in the Math Magic section. If necessary, simply plug the two angle values into the Fperpendicular equation and compare the results.

The force of gravity is neither in the direction of the acceleration nor perpendicular to it. The goal is always to have all forces directed perpendicular or parallel to each other and to the acceleration. So it is the habit on inclined plane problems such as this one to resolve the force of gravity into two components - one being parallel to the inclined plane and the other perpendicular to it. The formulas for resolving the force of gravity into its components are:
Fparallel= m • g • sine(Θ) 

Fperpendicular= m • g • cosine(Θ)


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