Railways Technical Ability Fluid Mechanics and Machinery Question Bank Fluid Mechanics

  • question_answer The displacement thickness at. Section, for an air stream \[\left( \rho \,\,=\,\,1.2\,\,\text{kg/}{{\text{m}}^{\text{3}}} \right)\] moving with a velocity of 10 m/s over a flat plate is 0.5 mm. What is the loss of mass rate of flow of air due to boundary layer formation in kg per meter width of plate per second?

    A) \[6\times {{10}^{-3}}\]            

    B) \[6\times {{10}^{-5}}\]

    C) \[3\times {{10}^{-3}}\]            

    D) \[2\times {{10}^{-3}}\]

    Correct Answer: A

    Solution :

    \[\delta *=0.5\,\,mm,\] \[\rho =1.2\,\,\text{kg/}{{\text{m}}^{\text{3}}}\text{,}\] \[u=10\,\text{m/s}\] Loss of mass rate of flow of air \[=\delta *\rho u\] \[=0.5\times {{10}^{-3}}\times 1.2\times 10=6\times {{10}^{-3}}\,\,\text{kg/m}\]

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