Main Question or Discussion Point
In the above case, mgcos(theta) is the component of gravity perpendicular to the surface of the wedge. Considering all surfaces to be frictionless, the horizontal component of the normal force would cause the wedge to accelerate towards the right, and the horizontal component mgcos(theta)-the horizontal component of the normal force on the block would be the net horizontal force on the block causing the block to move along with the wedge to the right. How is this possible? How can gravity cause a net horizontal acceleration?