A plane is traveling down a runway at 20 m/s. If the runway is 1000 meters long and the plane begins to accelerate at 10 m/s, how long does it take the plane to clear the runway?
Vi = 20 m/s
a = 10 m/s^2 note seconds squared
v = Vi + a t = 20 + 10 t
x = 0 + Vi t + (1/2) a t^2
1000 = 20 t + 5 t^2
5 t^2 + 20 t - 1000 = 0
t^2 + 4 t - 200 = 0
12.3 or about -16.3
so 12.3 seconds