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) → \((11, 4), \left(-\displaystyle\frac{31}{3}, -4\right)\)
Differentiating the curve with respect to time t (rates of change):
\( \displaystyle 6\frac{dx}{dt} = 3y^2\frac{dy}{dt} \)
The x coordinate changes 8 times as fast as y:
\( \displaystyle \frac{dx}{dt} = 8\frac{dy}{dt} \)
\( \displaystyle 48\frac{dy}{dt} = 3y^2\frac{dy}{dt} \)
The particle is moving, so \(\frac{dy}{dt} \ne 0\):
\(y^2 = 16,\quad y = \pm 4\)
The x coordinates from \(6x = y^3 + 2\):
\(y = 4:\ 6x = 66,\ x = 11\)
\( \displaystyle y = -4:\ 6x = -62,\ x = -\frac{31}{3} \)
So the points are (11, 4) and \(\left(-\frac{31}{3}, -4\right)\).