- #1
pointintime
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Homework Statement
A runner hopes to complet the 10,000 m run in less than 30.0 min. After running at constant speed for exactly 27.0 min, there are still 1100 m to go. The runner must tehn acceelerate at .20 s^2 m for how many seconds in order to achieve teh desired time?
Homework Equations
def of average velocity = t^-1 (X - Xo)
def of a = t^-1 (V - Vo)
Def of average velocity (when a is zero) = 2^-1 (V + Vo)
V = Vo + at
X = Xo + Vo t + 2^-1 a t^2
V^2 = Vo^2 + 2a(X - Xo)
The Attempt at a Solution
ok for the first part of the race I calculated his velocity has to be
5.494 s^-1 m
ok in order to calculate the time to accelerate for the last part of the race
I saw that
X = Xo + Vo t + 2^-1 a t^2
that would do me no good because I do not know the X value for we could stop accelerating and there are two t variables
V^2 = Vo^2 + 2a(X - Xo)
doesn't work becasue we don't know the V^2 at the end of the acceleration
def of a = t^-1 (V - Vo)
rearanged for t didn't work because we don't know the V at the end of the acceleration...
So I'm lost...