Hello. 1. The problem statement, all variables and given/known data There is a vertical cylinder-shaped reservoir full of water: Height h = 18 meters Radius R = 2 meters If suddenly a hole appeared on the bottom (radius r = 0.25 meters) how long would it take to empty the reservoir? 2. Relevant equations Probably related to Bernoulli's principle somehow someway. 3. The attempt at a solution To be honest with you I just reposted this problem from elsewhere. Some girl tried to solve it and since I am a pure mathematician I pretty much do not have a clue about those things. Tried to google it, but without proper knowledge did not succeed. Some kind of powerful formula and basic steps would be appreciated. Thanks.