OpenStax College Physics for AP® Courses, Chapter 7, Problem 28 (Test Prep for AP® Courses)

This is College Physics Answers with Shaun Dychko. We want to know how much gravitational potential energy is stored in the water due to its position in high up above the ground in the water tower. So the formula for calculating its potential energy is the mass of the water times gravitational field strength times the height on average or the height of its center of mass above the ground. So we need to figure out what mass there would be and suppose while there is 1.0 kilogram for every liter of water and suppose each person in the town served by this water tower requires 10 liters and there are maybe 10000 people served by a single water tower that would mean the tower has 100000 kilograms of water. Suppose the height of the tower is 10 meters and just using round numbers here because you know... that are correct within a degree or two of magnitude so to speak like you know... just put one with the correct number of zeroes is the closest we can expect to get in our guesses and this would mean the potential energy then will be 100000 kilograms—mass— times 10 newtons per kilogram you know, we can use 9.8 but given how much error there is in all of our other numbers, we can just use 10 to make our calculations easier and then multiply by 10 meters and this would make 10 million joules of gravitational potential energy in a water tower.