A particle moves along the curve $6x=y^3+2$. The points on the curve at which the $x$ coordinate is changing 8 times as fast as y coordinate are:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → $(11, 4),\left(-\frac{31}{3},-4\right)$
$6x=y^3+2$ [Given Curve]
$\frac{d}{dt}(6x)=\frac{d}{dt}(y^3+2)$
$6\frac{dx}{dt}=3y^2\frac{dy}{dt}$
and,
$\frac{dx}{dt}=3y^2\frac{dy}{dt}$ [Given]
$⇒6\left(8\frac{dy}{dt}\right)=3y^2\left(\frac{dy}{dt}\right)$
$⇒48\frac{dy}{dt}=3y^2\frac{dy}{dt}$
$⇒3y^2=48$
$⇒y=±4$
Substituting $±4$ in the given equation,
$6x=(±4)^3+2$
$⇒x=11$ and $x=-\frac{31}{3}$