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JEE Main & Advanced JEE Main Paper (Held on 7 May 2012)

  • question_answer
    If a circular iron sheet of radius 30 cm is heated such that its area increases at the uniform rate of\[6\pi c{{m}^{2}}hr,\]then the rate (in mm/hr) at which the radius of the circular sheet increases is   JEE Main Online Paper (Held On 07 May 2012)

    A) 1.0                                         

    B)                        0.1

    C)                        1.1                                         

    D)                        2.0

    Correct Answer: B

    Solution :

                    Let\[A=\pi {{r}^{2}}.\] \[\frac{dA}{dt}=2\pi r.\frac{dr}{dt}\]                       \[6\pi =2\pi (30).\frac{dr}{dt}\] \[\Rightarrow \]\[\frac{3}{30}=\frac{dr}{dt}\Rightarrow \frac{dr}{dt}=\frac{1}{10}=0.1\] Thus, the rate at which the radius of the circular sheet increases is 0.1


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