Question

The average height of an apple tree is 4.00 meters. How long would it take an apple falling from that height to reach the ground? Given: g = –9.8 meters/second2

Answer 1

We know, s = ut + 1/2gt²
In free-fall, u = 0
so, t = √2s/g

Now, substitute the values, 
t = √2*4 / 9.8   [ -ve sign shows opposite direction only ]
t = √8/ 9.8
t = 0.90 sec

In short, Your Answer would be 0.90 sec

Hope this helps!