Final answer:
In a 100 meter race, the displacement of the runner at the finish line is 100 meters, which is a vector quantity indicating how far and in what direction an object has moved from its starting position.
Step-by-step explanation:
The displacement of a runner when they reach the finish line in a 100 meter race is 100 meters. Displacement is defined as the vector distance from the initial position to the final position. In this case, since the runner has started from the starting line and ended at the 100 meter finish line without changing direction, the displacement is equal to the distance traveled, which is 100 meters.
For example, if a sprinter starts from rest and accelerates for 20 meters, then maintains a steady velocity for the remaining 80 meters of a 100-meter dash, the total displacement remains 100 meters, assuming they do not change direction. The displacement is always measured in a straight line from the start to the finish point, regardless of the path taken to get there. In the cases of athletes or objects moving with constant velocity, as with the Olympic-quality sprinter or marathon runners, their displacement can be easily calculated using their velocity and the time taken.