Question

If the runner completes exactly one lap what is her average speed? her average velocity? Explain your answer.

Answer 1

Average speed  =  (total distance covered) / (time to cover the distance).

Runner's average speed = (length of 1 lap) / (her time to run 1 lap).

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Average velocity =

           (straight-line distance between start-point and end-point)
divided by
           (time to go from start-point to end-point).

The runner's start-point and end-point are the same place.
The distance between them (her 'displacement') is zero. 
Her average velocity = zero .