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NEET Sample Paper NEET Sample Test Paper-13

  • question_answer
    A wind with speed 40 m/s blows parallel to the roof of a house. The area of the roof is \[250\text{ }{{m}^{2}}.\] Assuming that the pressure inside the house is atmospheric pressure, the force exerted by the wind on the roof and the direction of the force will be\[({{P}_{air}}=1.2\,kg/{{m}^{3}})\]

    A) \[4.8\times {{10}^{5}}N,\] downwards

    B)  \[4.8\times {{10}^{5}}N,\]upwards

    C)  \[2.4\times {{10}^{5}}N,\]upwards

    D) \[2.4\times {{10}^{5}}N,\] downwards

    Correct Answer: C

    Solution :

     Applying Bernoulli's theorem just above and just below the roof, \[P+\frac{1}{2}\rho {{v}^{2}}={{P}_{0}}+0\] \[({{P}_{0}}-P)=\frac{1}{2}\rho {{v}^{2}}=\Delta P\] Hence lift of the roof \[F=\Delta P.A=\frac{1}{2}\rho A{{v}^{2}}\] \[=\frac{1}{2}\times 1.2\times {{(40)}^{2}}\times 250=2.4\times {{10}^{5}}N\]


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