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## Homework Statement

Problem 3.7 Suppose that motion studies of a runner show that the maximum speed he

can maintain for a period of about 10 s is 12 m/s. If in a 100-m dash this runner

accelerates with constant acceleration until he reaches this maximum speed and then

maintains this speed for the rest of the race, what acceleration will he require if his total

time is 11 s?

## Homework Equations

a = v

^{2}/(22v - 200)

## The Attempt at a Solution

a = 2.25 m/s

^{2}

I've read through the solution. What I don't understand stand, however, is why v here would be the 12 m/s value. Sure, that's the velocity given, but how and why should I know to use 12 m/s? Why do I plug that into the relevant equation? I could say, sure, because it's the only velocity value given, but why that particular value?