Consider a simpler problem first: The ball on block with a constant incline. Assume the block is accelerated towards the +x direction and that the ball is not moving vertically on the block.
The ball will experience two forces: Its weight and a normal force coming from the incline [itex]W,\ N[/itex] . Assume the incline is at an angle [itex]\theta[/itex] w.r.t. the horizontal. What can you say that the acceleration will be given by in such a situation?