Q. If tangent to the curve $x = at^{2},\ y = 2at$ is perpandicular to $x$-axis, then its point of contact is

A) $(a,\ a)$
B) $(0,\ a)$
C) (0, 0)
D) $(a,\ 0)$
Explanation

(c)
Given, $x = at^{2}$ and $y = 2at$
$\therefore\ \ \ \ \frac{dx}{dt} = 2at$ and $\frac{dy}{dt} = 2a$
$\therefore$ Slope of tangent, $\left( \frac{dy}{dx} \right) = \frac{2a}{2at} = \frac{1}{t}$
$\Rightarrow \ \ \frac{1}{t} = \infty,\ \ \ \Rightarrow \ \ \ \ \ t = 0$ [given]
$\therefore$ Point of contact is (0, 0)

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.