Question

Bo Jackson was clocked at 4.12 seconds for running the 40 yard dash. how many miles per hour is this?

Answer 1

We have that Jackson took 4.12 seconds to run 40 yards, in other words, we have that Jackson moved at a speed of 9.71 yards a seconds, that is given by:

$S=\frac{40}{4.12}\Rightarrow S=9.708737864\Rightarrow S\approx9.71$

Now that we calculate the speed, we need to make a change of units and determine it using miles per hour.

We have that a mile is equivalent at 1760 yards, and an hour is equivalent at 3600 seconds, so we multiply the equivalencies with the speed we calculated before:

$S=\frac{40\text{yards}}{4.12\text{seconds}}\cdot\frac{1\text{mille}}{1760\text{yards}}\cdot\frac{3600\text{seconds}}{1\text{hour}}$

Now, we cancel the repeated units and operate:

Yards wil cancel each other out, same as seconds, and we will have:

$S=\frac{40}{4.12}\cdot\frac{1\text{mille}}{1760}\cdot\frac{3600}{1\text{hour}}\Rightarrow S=19.85878199$

From this, we have that Jackson moved at a speed of 19.86 miles per hour.