John Johnson set a world record for the "100.0" m run with a time of 9.86 s. If, after crossing the finish line, John walked directly back to his starting point in 90.9 s, what is the magnitude of his average velocity for the 200.0m?

Zero, since he ends up in the same place.

To find the magnitude of John's average velocity for the 200.0 m, we need to calculate the total displacement and divide it by the total time taken.

First, let's calculate the total displacement. John ran 100.0 m in one direction and then walked back to his starting point, which is a distance of 100.0 m in the opposite direction. So, the total displacement is the difference between these two distances:

Total displacement = 100.0 m - 100.0 m = 0 m

Since John ended up at his starting point, there is no net displacement.

Now, let's calculate the total time taken. John's running time was 9.86 s, and his walking time was 90.9 s. Thus, the total time taken is the sum of these two:

Total time taken = 9.86 s + 90.9 s = 100.76 s

Finally, we can calculate the average velocity by dividing the total displacement by the total time taken:

Average velocity = Total displacement / Total time taken
= 0 m / 100.76 s
= 0 m/s

Therefore, the magnitude of John's average velocity for the 200.0 m is 0 m/s.