Math Problem Statement

A bug is moving along the right side of the parabola y = x^2 at a rate such that its distance from the origin is increasing at 5 cm/min. a. At what rate is the x-coordinate of the bug increasing when the bug is at the point (1, 1)? b. Use the equation y = x^2 to find an equation relating dy/dt to dx/dt. c. At what rate is the y-coordinate of the bug increasing when the bug is at the point (1, 1)?

Solution

Let's go through each question one by one.

Given Information:

  • The bug moves along the parabola y=x2y = x^2.
  • The rate of increase in the distance from the origin (DD) is dDdt=5cm/min\frac{dD}{dt} = 5 \, \text{cm/min}.
  • We are asked about the rates of change in the xx- and yy-coordinates when the bug is at the point (1,1)(1, 1).

Part (a)

We need to find the rate of change of the xx-coordinate (dxdt\frac{dx}{dt}) when the bug is at (1,1)(1, 1).

  1. Distance from the origin DD is given by: D=x2+y2D = \sqrt{x^2 + y^2}
  2. Since y=x2y = x^2, substitute y=x2y = x^2 into the distance formula: D=x2+(x2)2=x2+x4=x1+x2D = \sqrt{x^2 + (x^2)^2} = \sqrt{x^2 + x^4} = x \sqrt{1 + x^2}
  3. Differentiate DD with respect to tt to find the relation between dDdt\frac{dD}{dt} and dxdt\frac{dx}{dt}: dDdt=ddt(x1+x2)\frac{dD}{dt} = \frac{d}{dt} \left( x \sqrt{1 + x^2} \right)
  4. Apply the product rule: dDdt=dxdt1+x2+xddt(1+x2)\frac{dD}{dt} = \frac{dx}{dt} \cdot \sqrt{1 + x^2} + x \cdot \frac{d}{dt} \left( \sqrt{1 + x^2} \right)
  5. To differentiate 1+x2\sqrt{1 + x^2}: ddt(1+x2)=121+x22xdxdt=xdxdt1+x2\frac{d}{dt} \left( \sqrt{1 + x^2} \right) = \frac{1}{2\sqrt{1 + x^2}} \cdot 2x \cdot \frac{dx}{dt} = \frac{x \frac{dx}{dt}}{\sqrt{1 + x^2}}
  6. Substitute back: dDdt=dxdt1+x2+xxdxdt1+x2\frac{dD}{dt} = \frac{dx}{dt} \sqrt{1 + x^2} + x \cdot \frac{x \frac{dx}{dt}}{\sqrt{1 + x^2}}
  7. Simplify: dDdt=dxdt(1+x2+x21+x2)\frac{dD}{dt} = \frac{dx}{dt} \left( \sqrt{1 + x^2} + \frac{x^2}{\sqrt{1 + x^2}} \right) dDdt=dxdt1+2x21+x2\frac{dD}{dt} = \frac{dx}{dt} \cdot \frac{1 + 2x^2}{\sqrt{1 + x^2}}
  8. Solve for dxdt\frac{dx}{dt}: dxdt=dDdt1+x21+2x2\frac{dx}{dt} = \frac{\frac{dD}{dt} \cdot \sqrt{1 + x^2}}{1 + 2x^2}
  9. Substitute x=1x = 1, dDdt=5\frac{dD}{dt} = 5: dxdt=51+121+212=523\frac{dx}{dt} = \frac{5 \cdot \sqrt{1 + 1^2}}{1 + 2 \cdot 1^2} = \frac{5 \cdot \sqrt{2}}{3}

Part (b)

Use the equation y=x2y = x^2 to relate dydt\frac{dy}{dt} and dxdt\frac{dx}{dt}:

  1. Differentiate both sides of y=x2y = x^2 with respect to tt: dydt=2xdxdt\frac{dy}{dt} = 2x \frac{dx}{dt}

Part (c)

To find dydt\frac{dy}{dt} at (1,1)(1,1):

  1. Substitute x=1x = 1 and dxdt=523\frac{dx}{dt} = \frac{5 \sqrt{2}}{3} into the equation: dydt=21523=1023cm/min\frac{dy}{dt} = 2 \cdot 1 \cdot \frac{5 \sqrt{2}}{3} = \frac{10 \sqrt{2}}{3} \, \text{cm/min}

Do you want details or have any questions about this solution?

Follow-up Questions:

  1. How would the calculations change if the bug's speed was given in terms of its yy-coordinate?
  2. What if the parabola had a different shape, such as y=x3y = x^3? How would that affect dydt\frac{dy}{dt}?
  3. How does the rate of change in distance relate to the rates of change in both xx and yy coordinates?
  4. Can you derive the rate of change formula if the bug moved along a circle instead?
  5. How would you interpret these rates of change in a real-world context?

Tip:

When dealing with related rates, always ensure each variable’s derivative is expressed with respect to the same independent variable, typically time tt.

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Math Problem Analysis

Mathematical Concepts

Related Rates
Derivatives
Distance Formula
Parabolic Motion

Formulas

D = sqrt(x^2 + y^2)
y = x^2
dD/dt = d/dt(x * sqrt(1 + x^2))
dy/dt = 2x * dx/dt

Theorems

Pythagorean Theorem
Chain Rule
Product Rule

Suitable Grade Level

Grades 11-12 or College Calculus