CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2010

  • question_answer
    An edge of a variable cube is increasing at the rate of 10 cm/s. How fast the volume of the cube will increase when the edge is 5 cm long?

    A)  \[750\text{ }c{{m}^{3}}/s\]        

    B)  \[75\,c{{m}^{3}}/s\]

    C)  \[300\text{ }c{{m}^{3}}/s\]     

    D)         \[150\,\,c{{m}^{3}}/s\]

    E)  \[25c{{m}^{3}}/s\]

    Correct Answer: A

    Solution :

    Let a be the edge of cube. Then,      \[\frac{da}{dt}=10\,cm/s\]         (Given) ...(i) \[\because \]Volume of cube is \[V={{a}^{3}}c{{m}^{3}}\] \[\Rightarrow \]               \[\frac{dV}{dt}=3{{a}^{2}}\frac{da}{dt}c{{m}^{3}}/s\] \[=3\times {{5}^{2}}\times 10c{{m}^{3}}/s\]          [using Eq. (i)] \[=750\,c{{m}^{3}}/s\]


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