Answer
(a) it will not reach this height.
(b) $1\ sec$
Work Step by Step
(a)
Step 1. Given $s=-16t^2+v_0t$, with $v_0=16$, we have $s=-16t^2+16t$
Step 2. To reach a height of $80\ ft$, we get $80=-16t^2+16t$ or $t^2-t+5=0$
Step 3. Let $a=1, b=-1, c=5$, use quadratic formula we found there is no real solution, meaning it will not reach this height.
(b) For reaching the ground, we have $s=0$, thus $-16t^2+16t=0$ which gives $t=0, 1\ sec$. Discard $t=0$ because it is the starting time, we have $t=1\ sec$
