Given data:
The expression for the height of the object is h= -16t^2 +144.
When the object hits the ground its height becomes zero.
[tex]\begin{gathered} h=0 \\ -16t^2+144=0 \\ -16t^2=-144 \\ t^2=9 \\ t=3,\text{ -3} \\ t=3\text{ s} \end{gathered}[/tex]Consider only positive value of time.
Thus, after 3 second object hit the ground.
