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## Main Question or Discussion Point

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 A

According to Bernoulli's equation: P

Setting P

Question: Which one is correct and why?

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 A

_{1}v_{1}= A_{2}v_{2}, since the cylinder has constant radius then A_{1}=A_{2}and so v_{1}= v_{2}.According to Bernoulli's equation: P

_{1}+ 0.5pv_{1}^{2}+ pgh_{1}= P_{2}+ 0.5pv_{2}^{2}+ pgh_{2}Setting P

_{1}= P_{2}= P_{0}(of atmosphere), h_{1}- h_{2}= H, we get v_{2}^{2}= v_{1}^{2}+ pgH which states clearly that v_{2}> v_{1}Question: Which one is correct and why?