Using the given function, it is found that the projectile hits the ground after 20 seconds.
It hits the ground when it's height, given by h(t), is equals to zero.
In this problem, the function that models it's height is given by:
h(t) = -4.9t^2 + 98t.
Then:
h(t) = 0
-4.9t^2 + 98t = 0.
-4.9t(t - 20) = 0
t - 20 = 0 -> t = 20.
The projectile hits the ground after 20 seconds.
More can be learned about functions at https://brainly.com/question/25537936