If the apple is on the ground, then the height y is 0. To find t, just plug in 0 for y:
[tex]0=-16t^{2}+120[/tex]
[tex]-120=-16t^{2} [/tex]
[tex] t^{2} =7.5[/tex]
[tex]t=2.74[/tex]
So the answer is 2.74 seconds.
Note that taking the square root of 7.5, mathematically, gives you both 2.74 and -2.74. But because we know that time did not go backwards, only the positive value for t was considered.
