Hi, Consider a vertical relatively long cylinder of constant radius open at both ends. We fill this cylinder with water and prevent water from falling down by a certain sheet as seen in the figure. Now suppose we remove the sheet suddenly. Let v1 be the speed of the upper surface of water, and v2 be the speed of the water at the bottom of the cylinder. According to the equation of continuity A1v1 = A2v2, since the cylinder has constant radius then A1=A2 and so v1 = v2. According to Bernoulli's equation: P1 + 0.5pv12 + pgh1 = P2 + 0.5pv22 + pgh2 Setting P1 = P2 = P0 (of atmosphere), h1 - h2 = H, we get v22 = v12 + pgH which states clearly that v2 > v1 Question: Which one is correct and why?