Slanted surfaces without friction: A box slides down a frictionless plane inclined at an angle θ above the horizontal. The gravitational force on the box is directed
A) parallel to the plane in the same direction as the movement of the box.
B) parallel to the plane in the opposite direction as the movement of the box.
C) perpendicular to the plane.
D) vertically.
E) at an angle θ below the inclined plane.

Question

Quizplus · Accepted Answer

The gravitational force is always directed vertically downwards. When the box is on the inclined plane, this force can be resolved into two components - one perpendicular to the plane and one parallel to the plane. The perpendicular component doesn't contribute to the motion of the box along the plane, so only the parallel component is relevant for this question. However, since the plane is frictionless, there is no force opposing the motion of the box along the plane. Therefore, the box will move downwards along the plane in the direction of the parallel component of the gravitational force, which is also vertically downwards.

Slanted Surfaces Without Friction: a Box Slides Down a Frictionless