Answer:
3.29 s
Step-by-step explanation:
We are given that
Height of building=240
Initial velocity=20ft/s
The height of the ball after t seconds is given by
[tex]h(t)=-16t^2-20t+240[/tex]
When the ball strike the ground then
h(t)=0
[tex]-16t^2-20t+240=0[/tex]
[tex]4t^2+5t-60=0[/tex]
Quadratic formula:
[tex]x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]
Using the quadratic formula
[tex]t=\frac{-5\pm\sqrt{25+960}}{8}[/tex]
[tex]t=\frac{-5\pm\sqrt{985}}{8}[/tex]
[tex]t=\frac{-5+31.28}{8}=3.29 s[/tex]
[tex]t=\frac{-5-31.38}{8}=-4.5[/tex]
Time cannot be negative .Therefore,
t=3.29 s
