2. Questions Bank
  3. JEE Main & Advanced
  4. Mathematics
  5. Applications of Derivatives

JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Critical Thinking

  • question_answer
    A man of height 1.8 metre is moving away from a lamp post at the rate of 1.2 \[m/\sec .\] If the height of the lamp post be 4.5 metre, then the rate at which the shadow of the man is lengthening is [MP PET 1989]

    A) \[0.4\,\,m/\sec \]

    B) \[0.8\,\,m/\sec \]

    C) \[1.2\,\,m/\sec \]

    D) None of these

    Correct Answer: B

    Solution :

    • \[\frac{dy}{dt}=1.2.\]According to the figure   \[x=\frac{2}{3}y\] Þ \[\frac{dx}{dt}=\frac{2}{3}.\frac{dy}{dt}\]           
    • \[\therefore \] Required rate of length of shadow \[\frac{dx}{dt}=0.8m/s\].


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