JEE Main & Advanced JEE Main Online Paper (Held on 9 April 2013)

  • question_answer
                                    Statement 1: The slope of the tangent at any point P on parabola, whose axis is the axis of \[x\] and vertex is the origin, is inversely proportional to the ordinate of the point P.                 Statement 2: The system of parabolas \[{{y}^{2}}=4ax\] satisfies a differential equation of degree 1 and order 1.      JEE Main Online Paper (Held On 09 April 2013)             

    A)                 Statement -1 is true, Statement -2 is true. Statement -2 is correct explanation for statement-1.                

    B)                 Statement -1 is true, Statement-2 is true. Statement -2 is not correct explanation for statement-1.                

    C)                 Statement -1 is false. Statement-2 is true.                

    D)                 Statement -1 is true. Statement-2 is false.                

    E)                 Statement -1 is false. Statement-2 is true.

    Correct Answer: B

    Solution :

                    Statement I Let the equation of parabola whose axis is the axis of x and vertex at the origin is \[{{y}^{2}}=4ax\]                 \[2y\frac{dy}{dx}=4a\,\,\,\Rightarrow \,\,\,\frac{dy}{dx}=\frac{2a}{y}\] \[\Rightarrow \]               \[\frac{dy}{dx}\propto \frac{1}{y}\]                 (where \[a\to \] parameter)                 Statement II \[{{y}^{2}}=4ax\]                     ...(i) \[\Rightarrow \]               \[2y\frac{dy}{dx}=4a\]\[\Rightarrow \,\,a=\frac{y}{2}\frac{dy}{dx}\]                       [from Eq.(i)]                 \[{{y}^{2}}=4x\cdot \,\frac{y}{2}\frac{dy}{dx}\] \[\Rightarrow \]               \[{{y}^{2}}=2xy\frac{dy}{dx}\] \[\Rightarrow \]               \[y=2x\frac{dy}{dx}\]     \[\therefore \] Order = 1 and degree = 1                


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