The initial kinetic energy is:
KEi = (1/2)m(vi)^2
The final kinetic energy is:
KEf = (1/2)m(vf)^2
The initial potential energy is:
PEi = mgh
The final potential energy is:
PEf = mg(0) = 0
Since energy is conserved:
KEf + PEf = KEi + PEi
(1/2)m(vf)^2 + 0 = (1/2)m(vi)^2 + mgh
Multiply both sides by 2 and divide both sides by m:
vf^2 = vi^2 + 2gh
Take the square root of both sides, and plug in given values:
vf = sqrt[vi^2 + 2gh] = sqrt[(66.0 m/s)^2 + 2(9.81 m/s^2)(25.0 m)] = 69.6 m/s
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