A crate of weight w is being pushed across a horizontal surface by a force directed at an angle of 20° below the horizontal.What is the magnitude of the normal force on the crate?
A)It is less than w.
B)It equals w.
C)It is more than w.
D)None of the above since the coefficient of kinetic friction is not given.

Question

Quizplus · Accepted Answer

The normal force is the perpendicular force exerted by the surface on the crate to support its weight. This force is equal in magnitude and opposite in direction to the weight of the crate. However, since the crate is being pushed at an angle below the horizontal, there is a horizontal component of the pushing force that opposes the static friction force, which in turn reduces the normal force. In other words, the crate is being pushed downwards as well as horizontally. Therefore, the normal force is less than the weight of the crate. However, since the pushing force is at an angle less than 90°, the normal force will be more than the vertical component of the pushing force. Ultimately, the normal force is greater than the weight of the crate, so the answer is C.

A Crate of Weight W Is Being Pushed Across a Horizontal