Look at its potential energy when it was in the tree. PE=mgh. We don't know the mass, m of the apple but that's ok. Assuming we can neglect air resistance, the potential energy will be fully converted into kinetic energy when it is just above the ground. The kinetic energy is KE=(1/2)mv². Setting these equal lets us cancel the mass:
[tex]mgh= \frac{1}{2}m v^{2} [/tex]
[tex]gh= \frac{1}{2} v^{2} [/tex]
[tex] v= \sqrt{2gh}= \sqrt{2(9.81)(2.3)}=6.717 \frac{m}{s} [/tex]
