Answer:
1.5 seconds
Step-by-step explanation:
You want to know when a ball launched from a height of 6 ft with a vertical velocity of 20 ft/s will hit the ground.
Ballistic motion
The equation for the height of the ball is ...
h(t) = -16t² +v0·t +h0
where v0 and h0 are the initial vertical velocity and height, respectively.
Application
For the given parameters, the equation is ...
h(t) = -16t² +20t +6
The solution to h(t) = 0 can be found using the quadratic formula:
0 = -16t² +20t +6 . . . . . . . a=-16, b=20, c=6
[tex]t=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}=\dfrac{-20\pm\sqrt{20^2-4(-16)(6)}}{2(-16)}\\\\\\t=\dfrac{20\pm\sqrt{784}}{32}=\dfrac{20\pm28}{32}=\{-0.25,1.5\}[/tex]
The ball will hit the ground after 1.5 seconds.
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