Question

what happen if the distance is negative

Answer 1

Distance" isn't a precise term because there are two different ways to describe it. One way, which is called in physics "displacement," means the difference between where you are now and where you were before. (or where the tip of a stick is compared to where its other end is.)  That's a vector, which means it has both magnitude (size) and direction.  So for instance, you can decide that anything pointing to the right is positive, and anything pointing to the left is negative, and then if you walk to the right, the displacement (the "distance") is positive, and if you go left, it's negative.  The other way to talk about distance is the size of the displacement, which would mean how many steps you took to get somewhere, or how many lines on a ruler between the beginning and end of your walk. That will never be negative.