Answer:
8 seconds
Step-by-step explanation:
Set the equation equal to 0. You do this because h(0) means that there is no height of the object, and that then implies that the object is on the ground (where there is no height). Then factor using the quadratic formula:
[tex]0=-5t^2+40t[/tex]
Factor out the common constant and variable between the terms:
[tex]0=-5t(t-8)[/tex]
Solving for t, you get that t = 0 and t = 8. The t = 0 is indicative of the fact that at zero seconds (in other words before the object was launched) it was still on the ground. At t = 8, it had completed its parabolic travels and landed on the ground again.
