Water enters through end A with speed v1 and leaves through end B with speed v2 of a cylindrical tube AB. The tube is always completely filled with water. In case I tube is horizontal and in case II it is vertical with end A upwards and in case III it is vertical with end B upwards We have v1=v2 for:

Explanation

The correct answer is Option D:According to the principle of conservation of mass, the flow rate of an incompressible fluid must be constant along a streamline. This means that the product of the cross-sectional area and the flow speed remains the same. Since the tube is completely filled with water and cylindrical, the cross-sectional area is constant, which means the speed at both ends must be equal (v1 = v2) in all orientations. In Options A, B, and C, although gravity influences the pressure within the tube, it does not change this fundamental requirement for incompressible flow in a closed system.