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A manufacturer has 200m2200m^{2} of sheet metal. What are the dimensions of the cylindrical tank of maximum volume that can be produced using this amount of sheet metal?

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Q. A manufacturer has 200m2200m^{2} of sheet metal. What are the dimensions of the cylindrical tank of maximum volume that can be produced using this amount of sheet metal?
  1. Understand the problem: Understand the problem.\newlineWe need to find the dimensions of a cylindrical tank (height hh and radius rr) that has the maximum volume, given that the surface area of the tank is 200m2200\,\text{m}^2. The surface area of a cylinder includes the area of the two circular ends and the area of the side. The formula for the surface area of a cylinder is A=2πr2+2πrhA = 2\pi r^2 + 2\pi rh, where AA is the surface area, rr is the radius, and hh is the height.
  2. Set up the equation: Set up the equation for the surface area.\newlineGiven that the surface area AA is 200m2200\,\text{m}^2, we can write the equation as:\newline200=2πr2+2πrh200 = 2\pi r^2 + 2\pi rh
  3. Express volume in terms of radius: Express the volume of the cylinder in terms of the radius.\newlineThe volume VV of a cylinder is given by the formula V=πr2hV = \pi r^2 h. We want to maximize this volume.
  4. Surface area equation for h: Use the surface area equation to express hh in terms of rr. From the surface area equation, we can solve for hh: 200=2πr2+2πrh200 = 2\pi r^2 + 2\pi rh h=2002πr22πrh = \frac{200 - 2\pi r^2}{2\pi r}
  5. Substitute hh into volume equation: Substitute the expression for hh into the volume equation.\newlineV=πr2×(2002πr22πr)V = \pi r^2 \times \left(\frac{200 - 2\pi r^2}{2\pi r}\right)\newlineSimplify the volume equation:\newlineV=200r2πr32V = \frac{200r - 2\pi r^3}{2}
  6. Differentiate volume equation: Differentiate the volume equation with respect to rr to find the critical points.dVdr=(2006πr2)2\frac{dV}{dr} = \frac{(200 - 6\pi r^2)}{2}Set the derivative equal to zero to find the critical points:0=(2006πr2)20 = \frac{(200 - 6\pi r^2)}{2}6πr2=2006\pi r^2 = 200r2=200(6π)r^2 = \frac{200}{(6\pi)}r=200(6π)r = \sqrt{\frac{200}{(6\pi)}}
  7. Calculate value of r: Calculate the value of r.\newliner=200(6π)r = \sqrt{\frac{200}{(6\pi)}}\newliner33.5103r \approx \sqrt{33.5103}\newliner5.787r \approx 5.787
  8. Verify critical point: Verify that the critical point is a maximum.\newlineTo ensure that the critical point we found corresponds to a maximum volume, we need to check the second derivative of the volume equation. However, since this is a problem that involves physical dimensions and we are looking for the maximum volume that can be created with a fixed surface area, we can reasonably assume that the critical point found is indeed a maximum. For a more rigorous approach, we would check the second derivative, but for this problem, we will proceed with the assumption that we have found the maximum.
  9. Calculate height using radius: Calculate the height hh using the radius rr.
    h=2002πr22πrh = \frac{200 - 2\pi r^2}{2\pi r}
    h=2002π(5.787)22π(5.787)h = \frac{200 - 2\pi(5.787)^2}{2\pi(5.787)}
    h2002π(33.5103)2π(5.787)h \approx \frac{200 - 2\pi(33.5103)}{2\pi(5.787)}
    h200210.27736.315h \approx \frac{200 - 210.277}{36.315}
    h10.27736.315h \approx \frac{-10.277}{36.315}
    h0.283h \approx -0.283

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