Question 6
A runner completes one full lap of a 400 m track in 50 s, finishing exactly where they started. What are their average speed and average velocity, in that order?
The right answer is the one marked above.
Average speed 8 m s-1, average velocity 0. Average speed is worked out from the total distance travelled:
average speed = 400 m ÷ 50 s = 8 m s-1
But the runner ends up at the very point they started from, so their displacement is zero. Velocity comes from displacement, so the average velocity = 0 ÷ 50 = 0.
This is the difference between distance and displacement at its sharpest — one is not zero while the other is.