Chapter 9 - Quadratic Functions and Equations - 9-1 Quadratic Graphs and Their Properties - Practice and Problem-Solving Exercises - Page 538: 27

$t\approx2.236$ seconds

The equation given is: $h = -16t^{2}+80$ We want to find when the stick hits the ground, so we want to calculate $t$ when $h$ is equal to 0. $0 = -16t^{2}$+80 $-80 = -16t^{2}$ $t^{2} = -\frac{80}{16}$ $t = \sqrt 5$ $t\approx2.236$ seconds