BCECE Engineering BCECE Engineering Solved Paper-2014

  • question_answer
    The sides of an equilateral triangle are increasing at the rate of 2 cm/s. The rate at which the area increases when the side is 10 cm, is

    A) \[\sqrt{3}c{{m}^{2}}/s\]

    B) \[10c{{m}^{2}}/s\]

    C) \[10\sqrt{3}c{{m}^{2}}/s\]

    D) \[\frac{10}{\sqrt{3}}c{{m}^{2}}/s\]

    Correct Answer: C

    Solution :

    Let \[x\] be the side of and equilateral triangle and A be the area. \[\therefore \]  \[A=\frac{\sqrt{3}}{4}{{x}^{2}}\] On differentiating both sides w. r. t. t, we get \[\frac{dA}{dt}=\frac{\sqrt{3}}{4}2x\frac{dx}{dt}\]                 Given, \[x=10cm\] and        \[\frac{dx}{dt}=2cm/s\] \[\therefore \]  \[\frac{dA}{dt}=\frac{\sqrt{3}}{4}2\times (10)\times 2\] \[=10\sqrt{3}c{{m}^{2}}/s\]                                


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