# Cross-Section of a Run, Part III

Recently I posted two photos of a runner taken 1.1 seconds apart and asked readers to speculate as to how fast he was running.  Here is a second proposed solution.

As I did in my first solution, I pasted the two photos together and took measurements of various lengths in pixels.

But this time, instead of estimating the runner’s height, I returned to the park and took a measurement of the distance between the white lines.  This distance is about 18 feet 9 inches in the park, and about 1250 pixels in the photo.

Thus, the 650 pixel distance between the runner’s two positions translates into about 9.75 feet.  If the runner is running 9.75 feet in 1.1 seconds, this scales to a speed of about 6.04 miles per hour.

The approximation of this runner’s mile is therefore around 9.93 minutes.  Pretty close to my first estimate.

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#### patrick honner

Math teacher in Brooklyn, New York

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