WB JEE Medical WB JEE Medical Solved Paper-2007

  • question_answer
    Radius of an air bubble at the bottom of the lake is r and it becomes 2r when the air bubble rises to the top surface of the lake. If P cm of water be the atmospheric pressure, then the depth of the lake is

    A)  2P                                         

    B)  8P

    C)  4P                                         

    D)  7P

    Correct Answer: D

    Solution :

                     Let depth of lake is \[x\,cm.\] \[\therefore \] \[{{P}_{1}}{{V}_{1}}={{P}_{2}}{{V}_{2}}\] \[(Pdg+xdg)\left( \frac{4}{3}\pi {{r}^{3}} \right)=Pdg\left[ \frac{4}{3}\pi {{(2r)}^{3}} \right]\] \[(P+x){{r}^{3}}=P(8{{r}^{3}})\] \[x=8P-P\]                 \[\Rightarrow \]               \[x=7P\]


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