* Displacement is the overall change in position from the starting point to the ending point. It's a vector quantity, meaning it has both magnitude and direction.

* The truck travels 2.5 km east to the quarry and then 2.5 km west back to its starting point.

* Since it ends up at the same location it started, the net change in position is zero.

Think of it like this: Imagine walking 10 steps forward and then 10 steps back. You've moved a total of 20 steps, but your displacement is 0 because you're back where you started.