Question

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Answer 1

The produced energy is E. To get this energy from the energy of falling water, apply energy conservation:

$$E=mgh,\\\space\\ m=\frac{E}{gh}=\frac E{9800}\text{ kg}.$$

The area of the5m-deep pond is

$$A=\frac Vd=\frac{m}{\rho d}=\frac{E}{49000000}\text{ m}^2.$$