Haryana PMT Haryana PMT Solved Paper-2011

  • question_answer
    A large number of liquid drops each of radius  a                 coalesce to form a single spherical drop of           radius b. The energy released in the process is              converted into the kinetic energy of the big        drop formed, the speed of the big drop is

    A) \[\sqrt{\frac{4T}{\rho }\left( \frac{1}{a}-\frac{1}{b} \right)}\]      

    B)  \[\sqrt{\frac{2T}{\rho }\left( \frac{1}{a}-\frac{1}{b} \right)}\]

    C) \[\sqrt{\frac{T}{\rho }\left( \frac{1}{a}-\frac{1}{b} \right)}\]        

    D)  \[\sqrt{\frac{6T}{\rho }\left( \frac{1}{a}-\frac{1}{b} \right)}\]

    Correct Answer: D

    Solution :

                    According to question                 \[\frac{4}{3}\pi {{a}^{3}}n=\frac{4}{3}\pi {{b}^{3}}\]                 \[n={{\left( \frac{b}{a} \right)}^{3}}\]                 \[W=T.4\pi [n{{a}^{2}}-{{n}^{2}}]\]                 \[W=\frac{1}{2}m{{v}^{2}}\]                 \[=\frac{1}{2}.\frac{4}{3}\pi {{b}^{3}}p{{v}^{2}}\]                 \[\therefore \] \[\frac{1}{2}\times \frac{4}{3}\pi {{b}^{3p{{v}^{2}}=}}T.4\pi [n{{a}^{2}}-{{b}^{2}}]\]                 or \[v=\sqrt{\frac{6T}{\rho }\left( \frac{n{{a}^{2}}}{{{b}^{3}}}-\frac{{{b}^{2}}}{{{b}^{3}}} \right)}\]                 \[\therefore \]  \[v=\sqrt{\frac{6T}{\rho }\left( \frac{1}{a}-\frac{1}{b} \right)}\]


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