What is the same about movibleand immovable?
Then you have two options: If the "unstoppable" objects stops, then it wasn't really unstoppable; and if the "immovable" object starts moving, then it wasn't really immovable. In the real world, there are no immovable or unstoppable objects. Any time two objects collide, the speed of both will change.
This is an exercise in logic. If an unstoppable force exists, then an immovable object cannot exist, because it would be able to be moved by the unstoppable force, and vice versa. Sideways Logic The unstoppable force does not "stop", the immovable object does not move : the unstoppable force ricochets off the immovable object!