an unstoppable force and an immovable object.
The force clearly passes straight through the object without the object even caring that the force existed. Solution found.
Now here is this one (three solutions)
You must pick one of two doors. One door will kill you, the other will save you. There are two guards, one that always lies and one that always tells the truth. You may only ask yes or no questions, and they can only respond with yes or no. You cannot already know the answer. You may ask only two questions. Best solution only needs one question.