How does the horizontal force affect the motion of an object on an inclined plane?

The horizontal force applied to an object on an inclined plane affects its motion by either speeding it up or slowing it down, depending on the direction of the force relative to the incline. If the force is parallel to the incline and in the same direction as the object's motion, it will accelerate the object. If the force is in the opposite direction, it will decelerate the object.