Math Problem Statement

An​ open-top cylindrical container is to have a volume 2197 cm^3. What dimensions​ (radius and​ height) will minimize the surface​ area? Question content area bottom Part 1 The radius of the can is about enter your response here cm and its height is about enter your response here cm.

Solution

To minimize the surface area of an open-top cylindrical container with a fixed volume, we can follow these steps:

  1. Define the Variables and Equations:

    • Let rr be the radius of the cylinder's base, and hh be its height.
    • The volume VV is given by: V=πr2hV = \pi r^2 h
    • Since the volume is given as V=2197cm3V = 2197 \, \text{cm}^3, we have: 2197=πr2h2197 = \pi r^2 h
    • The surface area SS for an open-top cylinder is: S=πr2+2πrhS = \pi r^2 + 2 \pi r h where πr2\pi r^2 is the area of the base and 2πrh2 \pi r h is the area of the side.
  2. Express hh in Terms of rr Using the Volume: h=2197πr2h = \frac{2197}{\pi r^2}

  3. Substitute hh in the Surface Area Formula: Substitute hh from the volume equation into the surface area formula: S=πr2+2πr(2197πr2)S = \pi r^2 + 2 \pi r \left( \frac{2197}{\pi r^2} \right) Simplifying, we get: S=πr2+4394rS = \pi r^2 + \frac{4394}{r}

  4. Minimize SS by Taking the Derivative with Respect to rr: Differentiate SS with respect to rr and set it to zero to find the critical points: dSdr=2πr4394r2=0\frac{dS}{dr} = 2 \pi r - \frac{4394}{r^2} = 0 Rearranging, we get: 2πr3=43942 \pi r^3 = 4394 r3=43942πr^3 = \frac{4394}{2 \pi} Solving for rr: r=43942π3r = \sqrt[3]{\frac{4394}{2 \pi}}

  5. Calculate rr and hh: Using this value of rr, calculate hh using h=2197πr2h = \frac{2197}{\pi r^2}.

Let's compute these values:The dimensions that will minimize the surface area are approximately:

  • Radius (r): 8.88 cm
  • Height (h): 8.88 cm

This symmetry between the radius and height results from minimizing the surface area for a given volume in an open-top cylindrical container.

Would you like more details on this solution, or have any questions?


Here are some additional questions you might explore:

  1. How would the dimensions change if the container had a closed top?
  2. How does the surface area change with small increases or decreases in volume?
  3. Could you use a different shape to hold the same volume with less surface area?
  4. What would be the surface area of this cylinder with the optimal dimensions?
  5. How does the optimization differ if the radius is fixed and height is variable?

Tip: In calculus, minimizing surface area with volume constraints often results in symmetrical dimensions, especially in shapes like cylinders.

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Math Problem Analysis

Mathematical Concepts

Calculus
Optimization
Geometry of Cylinders

Formulas

Volume of a cylinder: V = πr^2h
Surface area of an open-top cylinder: S = πr^2 + 2πrh
Derivative for finding minimum surface area

Theorems

Optimization using derivatives

Suitable Grade Level

Grades 11-12