Q. A particle moves along a parabolic path $y = {9x}^{2}$ in such a way that the $x$-componentes of velocity remains constant and has a value$\frac{1}{3}{ms}^{- 1}$. The acceleration of the projectile is

A) $\frac{1}{2}\widehat{\dot{\mathbf{j}}}\ {ms}^{- 2}$
B) $3\widehat{\dot{\mathbf{j}}}\ {ms}^{- 2}$
C) $\frac{2}{3}\widehat{\dot{\mathbf{j}}}\ {ms}^{- 2}$
D) $2\widehat{\dot{\mathbf{j}}}\ {ms}^{- 2}$
Explanation

(d) Given, equation is
$y = {9x}^{2}\ \ \ldots.(i)$
Since, $x$-component of velocity remains constant, we have
$\frac{dx}{dt} = \frac{1}{3}{ms}^{- 1}\ \ \ \ldots(ii)$
From Eq. (i), we have $y$-component of velocity.
$\frac{dy}{dt} = 18x \bullet \left( \frac{dx}{dt} \right)^{2}$
$\frac{dy}{dt} = 18\left( \frac{dx}{dt} \right)^{2} = 18 \times \left( \frac{1}{3} \right)^{2} = 2{ms}^{- 2}$
$\therefore\mathbf{a}_{y} = 2\ \widehat{\dot{\mathbf{j}}}\ {ms}^{- 2}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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