The motion of the apple is a free fall motion, so it is a uniformly accelerated motion. Therefore, we can use the following equation:

where
v=8 m/s is the speed of the apple when it hits the ground
u=0 is the initial speed of the apple
is the free-fall acceleration
h is the height from which the apple has fallen
Substituting data and rearranging the equation, we can find the height of the tree, h:
