AFMC AFMC Solved Paper-2005

  • question_answer
    If error in measurement of radius of sphere is 1%, what will be the error in measurement of volume?                          

    A) 1%                                         

    B) 1/3%         

    C) 3%                                         

    D) 10%          

    Correct Answer: C

    Solution :

    Key Idea: Volume of sphere is proportional to cube of radius. Let R be the radius of a sphere. Volume of sphere \[=\frac{4}{3}\pi {{R}^{3}}\] Taking log on both sides, we have \[\log \,V=log\frac{4}{3}\pi +\log \,{{R}^{3}}\] \[\log \,V=\log \frac{4}{3}\pi +3\log R\] In order to obtain change in volume, we differentiate both sides. \[\therefore \]                 \[\frac{\Delta V}{V}=\frac{3\Delta R}{R}\] \[\therefore \]   Percentage change in volume \[=3\times \]               percentage change in radius\[=3\times 1%=3%\]


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