BCECE Engineering BCECE Engineering Solved Paper-2005

  • question_answer
    Water is flowing in a pipe of diameter 4 cm with a velocity 3 m/s. The water then enters into a pipe of diameter 2 cm. The velocity of water in the other pipe is:

    A)  3 m/s                                   

    B)         6 m/s

    C)         12 m/s                                

    D)         8 m/s

    Correct Answer: C

    Solution :

    According to principle of continuity, when an incompressible and non-viscous liquid flows in a streamlined motion through a tube of non-uniform cross-section, then the product of the area of cross-section and the velocity of flow is same at every point in the tube. Thus,       \[Av\text{ }=\]constant or       \[{{A}_{1}}{{v}_{1}}={{A}_{2}}{{v}_{2}}\] or            \[\pi {{r}_{1}}{{\,}^{2}}{{v}_{1}}=\pi {{r}_{2}}{{\,}^{2}}{{v}_{2}}\] Given,   \[{{r}_{1}}=\frac{4}{2}cm=0.02\,m,\]                 \[{{r}_{2}}=\frac{2}{3}cm=0.01\,m,\] \[{{v}_{1}}=3\,m/s\]                 \[\therefore \]  \[\pi {{(0.02)}^{2}}\times 3=\pi {{(0.01)}^{2}}{{v}_{2}}\]                 or            \[{{v}_{2}}={{\left( \frac{0.02}{0.01} \right)}^{2}}\times 3\]                                 \[=12\,\,m/s\]


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