Question

An object is at rest on an inclined plane. In which direction does the static friction force act?

1) Opposite to the direction of the gravitational force
2) In the direction of the gravitational force
3) In the direction of the normal force
4) Along the surface of an inclined plane in an upward direction

Answer 1

Gravity pulls on the object in the downward direction. The normal force to the inclined plane points in a direction perpendicular to the surface of the plane. Then for the object to be at rest, the frictional force must act parallel to the inclined plane, pointing in the upward direction.