Question 11 of 82advanced🔧 ApplyNumerical4 marks

A particle moves along the curve 6y = x³ + 2. Find the points on the curve at which the y-coordinate is changing 8 times as fast as the x-coordinate.

Correct Answer

The required points on the curve are (4,11)(4, 11) and (−4,−313)\left(-4, \frac{-31}{3}\right).

Exercise: EXERCISE 6.1 | Q: 11 | (Page 5)
For More Understanding

Explanation

The problem is solved using the concept of related rates. As noted in the provided context, the rate of change of yy with respect to xx is calculated using the rates of change of yy and xx with respect to time tt. We differentiate the given curve equation with respect to tt and apply the given condition that the rate of change of yy is 8 times the rate of change of xx.

Solution Steps

  1. Step 1: Differentiate the equation of the curve 6y=x3+26y = x^3 + 2 with respect to time tt.

    6dydt=3x2dxdt6\frac{dy}{dt} = 3x^2 \frac{dx}{dt}
  2. Step 2: Apply the given condition. The problem states that the yy-coordinate changes 8 times as fast as the xx-coordinate, which means dydt=8dxdt\frac{dy}{dt} = 8 \frac{dx}{dt}. Substitute this into the differentiated equation:

    6(8dxdt)=3x2dxdt6\left(8 \frac{dx}{dt}\right) = 3x^2 \frac{dx}{dt}
  3. Step 3: Simplify the equation to solve for xx. Assuming dxdt≠0\frac{dx}{dt} \neq 0, we can divide both sides by dxdt\frac{dx}{dt}:

    48=3x248 = 3x^2 x2=16x^2 = 16 x=±4x = \pm 4
  4. Step 4: Find the corresponding yy-coordinates by substituting the values of xx into the original curve equation 6y=x3+26y = x^3 + 2. For x=4x = 4:

    6y=(4)3+2=64+2=666y = (4)^3 + 2 = 64 + 2 = 66 y=11y = 11

    Point is (4,11)(4, 11).

    For x=−4x = -4:

    6y=(−4)3+2=−64+2=−626y = (-4)^3 + 2 = -64 + 2 = -62 y=−313y = \frac{-31}{3}

    Point is (−4,−313)\left(-4, \frac{-31}{3}\right).