Water falls from a 40 m high dam at the rate of 9 × 10^4 kg per hour. Fifty percentage of gravitational potential energy can be converted into…

Water falls from a $\displaystyle 40$ m high dam at the rate of $\displaystyle 9 \times 10^4 \mathrm{~kg}$ per hour. Fifty percentage of gravitational potential energy can be converted into electrical energy. Using this hydro electric energy number of $\displaystyle 100$ W lamps, that can be lit, is : (Take $\displaystyle \mathrm{g}=10 \mathrm{~ms}^{-2}$ )