The time taken by the ball to hit the ground is required.
The time taken by the ball to hit the ground is 2 seconds.
u = Initial velocity = 30 feet per second
h = Initial height = 4 feet
t = Time taken
g = Acceleration due to gravity = [tex]-32\ \text{feet/s}^2[/tex]
From the equations of kinematic motion we get
[tex]0=h+ut+\dfrac{1}{2}gt^2\\\Rightarrow 0=4+30t+\dfrac{1}{2}(-32)t^2\\\Rightarrow -32t^2+60t+8=0\\\Rightarrow t=\dfrac{-60\pm \sqrt{60^2-4\left(-32\right)\times8}}{2\left(-32\right)}\\\Rightarrow t=-0.125,2[/tex]
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