A total of 104 kg of water per second flows over a waterfall 50 m high. If half of the power this flow represents could be converted into electricity, how many 50-W lightbulbs could be supplied?

the converted energy per second (watts) is ... 1/2 * m * g * h

bulbs supplied is ... 1/2 * 104 * 9.81 * 50 / 50