JIPMER Jipmer Medical Solved Paper-2010

  • question_answer
    64 spherical rain drops of equal size are falling vertically through air with a terminal velocity\[1.5\text{ }m{{s}^{-1}}\]. If these drops coalesce to form a big spherical drop, then terminal velocity of big drop is

    A)  \[8\,m{{s}^{-1}}\]         

    B)                        \[16\,m{{s}^{-1}}\]        

    C)         \[24\,m{{s}^{-1}}\]                        

    D)         \[32\,m{{s}^{-1}}\]

    Correct Answer: C

    Solution :

    Volume of big drop \[=64\times \] volume of a small drop \[\Rightarrow \]               \[\frac{4}{3}\pi {{R}^{3}}=64\times \frac{4}{3}\pi {{r}^{3}}\Rightarrow R=4r\] The terminal velocity of spherical rain drop \[v=\frac{2{{r}^{2}}(\rho -\sigma )}{9\eta }\Rightarrow v\propto {{r}^{2}}\] \[\Rightarrow \]               \[\frac{{{v}_{1}}}{{{v}_{2}}}={{\left( \frac{r}{R} \right)}^{2}}={{\left( \frac{1}{4} \right)}^{2}}=\frac{1}{16}\] \[\therefore \]  \[{{v}_{2}}=16{{v}_{1}}=16\times 1.5=24\,m{{s}^{-1}}\]


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