Sunlight will be the answer
may be
(if you will provide a little more information about your question.....
it will be easy to give the answer)
When we can get the Kinetic energy from this formula KE= 1/2 M V^2
and we can get the potential energy from this formula PE = M g H
we can set that the kinetic energy at the bottom of the fall equals the potential energy at the top so,
KE = PE
1/2 MV^2 = M g H
1/2 V^2 = g H
when V is the velocity, g is an acceleration of gravitational force and H is the height of the fall.
∴ v^2 = 2 * 9.8 * 8 = 156.8
∴ v= √156.8 = 12.5 m/s
