KCET · Maths · Application of Derivatives
In a Mahakumbh, a drone camera is moving along \(3y = x^3 - 3\). When \(y\)-coordinate changes \(9\) times as fast as \(x\)-coordinate, it captures good quality pictures. Then one of the precise positions of the drone at that instant is
- A \((-3, -8)\)
- B \((3, -8)\)
- C \((3, 8)\)
- D \((-3, 8)\)
Answer & Solution
Correct Answer
(C) \((3, 8)\)
Step-by-step Solution
Detailed explanation
The equation of the curve is given by \(3y = x^3 - 3\).
Differentiating both sides with respect to time \(t\), we get:
\(3 \dfrac{dy}{dt} = 3x^2 \dfrac{dx}{dt}\)
\(\dfrac{dy}{dt} = x^2 \dfrac{dx}{dt}\)
Given that the \(y\)-coordinate changes \(9\) times as fast as the \(x\)-coordinate:
\(\dfrac{dy}{dt} = 9 \dfrac{dx}{dt}\)
Equating the two expressions for \(\dfrac{dy}{dt}\):
\(x^2 \dfrac{dx}{dt} = 9 \dfrac{dx}{dt}\)
Assuming \(\dfrac{dx}{dt} \neq 0\), we get \(x^2 = 9\), which gives \(x = 3\) or \(x = -3\).
For \(x = 3\), substituting into the curve equation gives \(3y = (3)^3 - 3 = 24 \Rightarrow y = 8\). The point is \((3, 8)\).
For \(x = -3\), substituting into the curve equation gives \(3y = (-3)^3 - 3 = -30 \Rightarrow y = -10\). The point is \((-3, -10)\).
Among the given options, \((3, 8)\) is the correct position.
Answer: \((3, 8)\)
Differentiating both sides with respect to time \(t\), we get:
\(3 \dfrac{dy}{dt} = 3x^2 \dfrac{dx}{dt}\)
\(\dfrac{dy}{dt} = x^2 \dfrac{dx}{dt}\)
Given that the \(y\)-coordinate changes \(9\) times as fast as the \(x\)-coordinate:
\(\dfrac{dy}{dt} = 9 \dfrac{dx}{dt}\)
Equating the two expressions for \(\dfrac{dy}{dt}\):
\(x^2 \dfrac{dx}{dt} = 9 \dfrac{dx}{dt}\)
Assuming \(\dfrac{dx}{dt} \neq 0\), we get \(x^2 = 9\), which gives \(x = 3\) or \(x = -3\).
For \(x = 3\), substituting into the curve equation gives \(3y = (3)^3 - 3 = 24 \Rightarrow y = 8\). The point is \((3, 8)\).
For \(x = -3\), substituting into the curve equation gives \(3y = (-3)^3 - 3 = -30 \Rightarrow y = -10\). The point is \((-3, -10)\).
Among the given options, \((3, 8)\) is the correct position.
Answer: \((3, 8)\)
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