Question 1206150
A ball is thrown vertically upward with an initial velocity of 48 feet per second. The distance s​ (in feet) of the ball from the ground after t seconds is s=48t−16t2
.
(a) At what time t will the ball strike the​ ground?

at t=0 the ball is on ground

S(t)=0 = 48t-16t^2

Solve for t

16t^2=48t

t=3s

​(b) For what time t is the ball more than 20 feet above the​ ground?

Between two times it is above 20 ft

48t-16t^2 >20

Solve the inequality  to get the time (s)

*[illustration projectile1.png].