Two identical balls roll across the top of a table on parallel paths. One of the balls has to roll down into and up out of a dip in the table. The other ball rolls on the flat all the time. Which ball gets to the far side of the table first, and why?.
If the tabletop is flat, we must add a condition that the balls are set in motion by identical forces. We must ignore friction, since not specified. We must also assume the "dip" is not so great that the ball encountering it cannot climb the other side (perhaps that is implied by problem statement). In these cases I think the ball going thru the dip will arrive first (same horizontal distance but greater average speed with the dip). Perhaps other variables need to be specified or assumed.