Question

Water coming out of the mouth of a tap and falling vertically in streamline flow forms a tapering, column, i.e., the area of crosssection of the liquid column decreases as it moves down. Which of the following is the most accurate explanation for this

Options :

  1. As the water moves down, its speed increases and hence its pressure decreases. It is then compressed by the atmosphere

  2. Falling water tries to reach a terminal velocity and hence reduces the area of crosssection to balance upward and downward forces

  3. 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 × area, the area decreases as velocity increases

  4. The surface tension causes the exposed surface area of the liquid to decrease continuously

Show Answer

Answer :

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 × area, the area decreases as velocity increases

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