Water coming out of the mouth of a tap and falling vertically in streamline flow forms a tapering column, i.e., the area of cross-section of the liquid column decreases as it moves down. Which of the following is the most accurate explanation for this?
(a) As the water moves down, its speed increases and hence its pressure decreases. It is then compressed by the atmosphere.
(b) Falling water tries to reach a terminal velocity and hence reduces the area of cross-section to balance upward and downward forces.
(c) The mass of water flowing past any cross-section must remain constant. Also, water is almost incompressible. Hence, the rate of volume flow must remain constant. As this is equal to velocity x area, the area decreases as velocity increases.
(d) The surface tension causes the exposed surface area of the liquid to decrease continuously.
