A100-meter sprint is a race using only the straight side of a racetrack. a 400-meter sprint is a race that makes one complete lap around a racetrack. why are velocity and speed the same for a 100-m sprint but not a 400-m sprint?

Speed is a scalar quantity (meaning it can be measured using a single number that represents the amount), while velocity is composed of the scalar quantity plus the direction. As the 100-meter sprint only takes place in one direction, the speed and velocity for this is just the same. For the 400-meter sprint however, the direction of your speed changes as you turn for her curved part of the race. Therefore, a direction change is happening.