JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Morning)

  • question_answer
     A liquid of density \[\rho \] is coming out of a hose pipe of radius a with horizontal speed v and hits a mesh. 50% of the liquid passes through the mesh unaffected. 25% looses all of its momentum and 25% comes back with the same speed. The resultant pressure on the mesh will be [JEE Main Online Paper (Held On 11-Jan-2019 Morning]

    A) \[\rho {{v}^{2}}\]                                           

    B) \[\frac{1}{4}\rho {{v}^{2}}\]

    C) \[\frac{3}{4}\rho {{v}^{2}}\]   

    D)                  \[\frac{1}{2}\rho {{v}^{2}}\]

    Correct Answer: C

    Solution :

    The momentum per second carried by liquid per second is \[\rho {{v}^{2}}A.\] [A is area of cross section of pipe] The force exerted due to reflected back molecules \[2\left( \frac{1}{4}\rho a{{v}^{2}} \right)\] So, the resultant pressure is \[\frac{\left( \frac{1}{2}\rho A{{v}^{2}}+\frac{1}{4}\rho A{{v}^{2}} \right)}{A}=\frac{3}{4}\rho {{v}^{2}}\]


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