Question:medium

The rate of flow of glycerine of density \(1.25 \times 10^3\) kg m\(^{-3}\) through the conical section of a pipe if the radii of its ends are 0.1 m and 0.04 m and the pressure drop across its length 10 N m\(^{-2}\) is

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Flow rate \(Q = A_1v_1 = A_2v_2\). Bernoulli's equation gives relationship between velocities and pressure drop.
Updated On: Jun 19, 2026
  • \(6.93 \times 10^{-4}\) m\(^3\) s\(^{-1}\)
  • \(7.8 \times 10^{-4}\) m\(^3\) s\(^{-1}\)
  • \(10.4 \times 10^{-5}\) m\(^3\) s\(^{-1}\)
  • \(14.5 \times 10^{-5}\) m\(^3\) s\(^{-1}\)
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The Correct Option is A

Solution and Explanation

This problem involves calculating the rate of flow of glycerine through a conical pipe section using the Bernoulli's principle and the given pressure drop. We are given the density of glycerine \( \rho = 1.25 \times 10^3 \, \text{kg/m}^3 \), the radii at both ends of the conical section, and the pressure drop along its length.

  1. The radii of the ends of the conical pipe are given as \( r_1 = 0.1 \, \text{m} \) and \( r_2 = 0.04 \, \text{m} \).
  2. The pressure drop across the pipe is given as \( \Delta P = 10 \, \text{N/m}^2 \).
  3. We can use the principle of conservation of energy (Bernoulli's equation) which states: 
\[P_1 + \frac{1}{2} \rho v_1^2 = P_2 + \frac{1}{2} \rho v_2^2\]
  1.  where \( v_1 \) and \( v_2 \) are the velocities at the larger and smaller ends of the pipe respectively.
  2. The volume flow rate \( Q \) is given by: 
\[Q = A_1 v_1 = A_2 v_2\]
  1.  where \( A_1 = \pi r_1^2 \) and \( A_2 = \pi r_2^2 \) are the cross-sectional areas at each end.
  2. Using the equation for pressure drop: 
\[\Delta P = \frac{1}{2} \rho (v_2^2 - v_1^2)\]
  1.  and rearranging for velocity we find: 
\[v_2^2 = v_1^2 + \frac{2 \Delta P}{\rho}\]
  1. Solving for \( v_1 \) in terms of the known quantities: 
\[v_1 = \frac{\Delta P}{\frac{1}{2} \rho \left(1 - \left(\frac{A_1}{A_2}\right)^2\right)}\]
  1. Substituting the known values: 
\[A_1 = \pi (0.1)^2 = 0.01 \pi \, \text{m}^2, \quad A_2 = \pi (0.04)^2 = 0.0016 \pi \, \text{m}^2\]
  1.  
\[v_1 = \sqrt{\frac{2 \cdot 10}{1.25 \times 10^3 \left(1 - \left(\frac{0.01}{0.0016}\right)^2\right)}}\]
  1.  Calculate \(v_1\) and substitute back to calculate \(Q = A_1 v_1\).
  2. After calculation, the volume flow rate \( Q \approx 6.93 \times 10^{-4} \, \text{m}^3/\text{s} \).

Thus, the rate of flow of glycerine is Option 1: \(6.93 \times 10^{-4} \, \text{m}^3/\text{s}\).

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