Suppose I point a garden hose upwards and turn on the tap. The water flies to a certain height. Now suppose I constrict the opening of the hose. Now the water flies to a greater height. I understand that this is because of the increased kinetic energy of the water coming out of the hose.But isn't the total energy of the water due to height of the overhead water tank?Therefore if I haven't changed the height of the tank, where did this extra energy come from?

Question

mani_jha · Answer

The work you do to stop a part of the water from coming out of the hose is utilized as kinetic energy to increase the velocity of the remaining water that comes out. According to the equation of continuity, lower area of cross section must have a high velocity of fluid coming out through it.

anonymous · Answer

yes totally agree with manijha there is an external force given by YOU when the water comes out
In the absence of non-conservative forces, mechanical energy is conserved
morever the increased speed is as same amount of water now has to go through a smaller cross-sectional area equation of continuity