Answer:
t = 5 seconds
Step-by-step explanation:
It is given that, the height h, in feet of a ball above the ground is given by :
[tex]h=-16t^2+64t+80[/tex]
Where t is in seconds
We need to find how long does it take the ball to hit the ground? When it hits the ground, its height will be equal to 0. So,
[tex]-16t^2+64t+80=0\\\\t=\dfrac{-64\pm \sqrt{(64)^2-4\times (-16)(80)} }{2\times -16}\\\\t=\dfrac{-64+ \sqrt{(64)^2-4\times (-16)(80)} }{2\times -16},\dfrac{-64-\sqrt{(64)^2-4\times (-16)(80)} }{2\times -16}\\\\t=-1\ s\ \text{and}\ t=5\ s[/tex]
Neglecting negative time.
It means ball will take 5 seconds to hit the ground.
