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If a huge tank has a small side hole at a depth of 2 m from the surface of water, then the velocity of water flowing through the hole is \((g = 10ms^{-2})\)

  • A.\(2\sqrt{5}ms^{-1}\)
  • B.\(2\sqrt{10}ms^{-1}\)
  • C.\(\sqrt{10}ms^{-1}\)
  • D.\(4\sqrt{10}ms^{-1}\)
  • E.\(4\sqrt{5}ms^{-1}\)

Answer: B

The velocity is \(2\sqrt{10}\) m s-1.

By Torricelli's theorem, water leaves a small hole at depth \(h\) below the free surface with speed \(v = \sqrt{2gh}\), the speed of a body falling freely through \(h\). In a huge tank the surface barely moves, so its speed can be ignored.

\[ \begin{aligned} v &= \sqrt{2 \times 10 \times 2} = \sqrt{40} \\ &= 2\sqrt{10} \text{ m s}^{-1} \end{aligned} \]

\(2\sqrt{5} = \sqrt{20}\) is \(\sqrt{gh}\), which drops the factor 2, and \(\sqrt{10}\) is smaller still.

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