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

  • question_answer
    A population p(t) of 1000 bacteria introduced into nutrient medium grows according to the relation \[p(t)=1000+\frac{1000t}{100+{{t}^{2}}}\]. The maximum size of this bacterial population is [Karnataka CET  2005]

    A)            1100

    B)            1250

    C)            1050

    D)            5250

    Correct Answer: C

    Solution :

               \[p(t)=1000+\frac{1000t}{100+{{t}^{2}}}\]                    \[\frac{dp}{dt}=\frac{(100+{{t}^{2}})\,1000-1000t\,.\,2t}{{{(100+{{t}^{2}})}^{2}}}\]\[=\frac{1000\,(100-{{t}^{2}})}{{{(100+{{t}^{2}})}^{2}}}\]                    For extremum, \[\frac{dp}{dt}=0\Rightarrow t=10\]                    Now \[{{\left. \frac{dp}{dt} \right|}_{t\,<\,10}}>0\] and \[{{\left. \frac{dp}{dt} \right|}_{t\,>\,10}}<0\]                    \ At \[t=10\], \[\frac{dp}{dt}\]change from positive to negative.                    \ p is maximum at \[t=10\].                    \ \[{{p}_{\max }}=p(10)=1000+\frac{1000.10}{100+{{10}^{2}}}=1050\].


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