A manufacturer has 200m2 of sheet metal. What are the dimensions of the cylindrical tank of maximum volume that can be produced using this amount of sheet metal?
Q. A manufacturer has 200m2 of sheet metal. What are the dimensions of the cylindrical tank of maximum volume that can be produced using this amount of sheet metal?
Understand the problem: Understand the problem.We need to find the dimensions of a cylindrical tank (height h and radius r) that has the maximum volume, given that the surface area of the tank is 200m2. 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+2πrh, where A is the surface area, r is the radius, and h is the height.
Set up the equation: Set up the equation for the surface area.Given that the surface area A is 200m2, we can write the equation as:200=2πr2+2πrh
Express volume in terms of radius: Express the volume of the cylinder in terms of the radius.The volume V of a cylinder is given by the formula V=πr2h. We want to maximize this volume.
Surface area equation for h: Use the surface area equation to express h in terms of r. From the surface area equation, we can solve for h: 200=2πr2+2πrhh=2πr200−2πr2
Substitute h into volume equation: Substitute the expression for h into the volume equation.V=πr2×(2πr200−2πr2)Simplify the volume equation:V=2200r−2πr3
Differentiate volume equation: Differentiate the volume equation with respect to r to find the critical points.drdV=2(200−6πr2)Set the derivative equal to zero to find the critical points:0=2(200−6πr2)6πr2=200r2=(6π)200r=(6π)200
Calculate value of r: Calculate the value of r.r=(6π)200r≈33.5103r≈5.787
Verify critical point: Verify that the critical point is a maximum.To 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.
Calculate height using radius: Calculate the height h using the radius r. h=2πr200−2πr2 h=2π(5.787)200−2π(5.787)2 h≈2π(5.787)200−2π(33.5103) h≈36.315200−210.277 h≈36.315−10.277 h≈−0.283
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