JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Application in Mechanics and Rate Measurer

  • question_answer
    The edge of a cube is increasing at the rate of \[5cm/\sec .\]How fast is the volume of the cube increasing when the edge is 12cm long

    A)            \[432\,c{{m}^{3}}/\sec \]

    B)            \[2160\,c{{m}^{3}}/\sec \]

    C)            \[180\,c{{m}^{3}}/\sec \]

    D)            None of these

    Correct Answer: B

    Solution :

               Let velocity \[v=5\,cm/\sec \]            (Increasing the rate/sec is called the velocity)                    \[\frac{da}{dt}=5\]                                                       .....(i)            Where a is distance and t is time.            But if a is edge of a cube, then \[V={{a}^{3}}\]            Differentiating w.r.t. time t, so            \[\frac{dV}{dt}=3{{a}^{2}}\frac{da}{dt}=3{{a}^{2}}.5\,=\,15{{a}^{2}}=15\times {{(12)}^{2}}\]                   \[=2160\,\,c{{m}^{3}}/\sec \]    (\[\because \]edge \[a=12\,cm)\].


You need to login to perform this action.
You will be redirected in 3 sec spinner