A container is full of water. A hole of cross section area a exists at the wall of the container, x height beneath the surface of water. (So speed would be v = √(2gx). Let's call it v for now). The density of water is ρ.Then why would the force imparted by the water gushing out of the hole on the container be F = av2ρ? I understand it has something to do with change in momentum, per unit time. But when I calculate it that way, I am not able to find change in momentum per unit time but just momentum per unit time. So the way I do it is: Volume of water water flowing out per second: av (assuming that velocity is per second) Mass of water flowing out per second: avρ Momentum of water flowing out per second: avρv = av2ρ But we haven't computed the (change in momentum/time) but just (momentum/time). So would the answer still be valid?