2. Sample Papers
  3. JEE Main & Advanced

JEE Main & Advanced Sample Paper JEE Main Sample Paper-35

  • question_answer
    An aeroplane flying with uniform speed horizontally 1 kilometre above the ground is observed at an elevation of\[{{60}^{o}}\]. After 10 seconds if elevation is observed to be \[{{30}^{o}}\], then the speed of the plane (in kilometre /hour) is

    A)  \[\frac{240}{\sqrt{3}}\]                                

    B)  \[200\sqrt{3}\]

    C)  \[240\sqrt{3}\]                

    D)  \[\frac{120}{\sqrt{3}}\]

    Correct Answer: C

    Solution :

    Equation of tangent with slope \[=\frac{-3}{4},\,\] is \[y=\frac{-3}{4}x+C\] Now, \[C=\sqrt{32\times {{\left( \frac{-3}{4} \right)}^{2}}+18}\,=\sqrt{18+18}=6\] (Using condition of tangency) \[\therefore \,\,y=\frac{-3}{4}\,x+6\,\Rightarrow \,3x+4y\,=24\] It meets the coordinate axes in A and B. So A (8, 0) and B(0, 6) Hence, required area \[\Delta AOB=\frac{1}{2}\,(8)\,(6)=24\]


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