## Essential University Physics: Volume 1 (4th Edition)

We know that $U=mgh$ We plug in the known values to obtain: $U=(8.5\times 10^9)(9.8)(140)=1.166\times 10^{13}J$ We can find the electricity as $E=Pt$ We plug in the known values to obtain: $E=(330\times 10^6)(8.0\times 3600)=9.504\times 10^{12}J$ The efficiency is given as: $\epsilon=\frac{E}{U}\times 100=\frac{9.504\times 10^{12}}{1.166\times 10^{13}}\times 100=81\%$