Assuming this is a 2D game, you should look into the "Graphics View Framework":http://qt-project.org/doc/qt-4.8/graphicsview.html
When you use the QGraphicsItem as base class for your viewable items, you get the collision detection algorithm for free. Allthough not the top of the edge, it will satisfy your needs.
You should check the "Colliding Mice example":http://qt-project.org/doc/qt-4.8/examples-graphicsview.html
It will show you how to move items etc, also look at Asteroids.
The logic behind the original arcanoid, was very simple towards ball movement. It will change the velocity of the ball depending on the collision location (left, middle, right).
I think you have enough to look at, so get started.