Hi Please have a look on the attachment. Do you also agree that the shell strikes the water at the same speed? It seems false to me. The vertical and horizontal motion is independent of each other. When the shell is fired horizontally, it starts descending toward the ground from less height compared to the other case. It's kinetic energy is used to push the shell horizontally against air resistance. On the other hand, when the shell is fired at an angle, it's kinetic energy has two components. One component pushes it forward horizontally and the other component pushes it vertically against the gravitational force . In this case the shell descends toward the ground from greater height and hence more kinetic energy at the moment when it strikes water. Thank you.