a cone is constructed by cutting a sector from a circular sheet of metal with radius 20. the cut sheet is then folded up and welded (see figure). find the radius and height of the cone with maximum volume that can be formed in this way.



Answer :

The radius of the cone is 16.33, the height of the cone is 11.55, and the maximum volume of the cone is 1,026.67[tex]\pi[/tex].

How to find volume of the cone?

Given

metal radius = R = 20

cone base radius = r

cone height = h

First, we can use Pythagoras theorem

R^2 = r^2 + h^2

r^2 = R^2 - h^2

r^2 = 400 - h^2

Then, we use volume of cone formula

V = 1/3[tex]\pi[/tex] * r^2 * h

V = 1/3[tex]\pi[/tex] * (400 - h^2) * h

V = 1/3[tex]\pi[/tex] * 400h - h^3

To get maximum volume of cone, V'(h) must be 0. So,

1/3[tex]\pi[/tex] * 400 - 3h^2 = 0

400 - 3h^2 = 0

3h^2 = 400

h^2 = 400/3

h = [tex]\frac{20}{\sqrt{3}}[/tex] or 11.55

Next, we find the r with substitution method. So,

r^2 = 400 -  ([tex]\frac{20}{\sqrt{3}}[/tex]    )^2

r^2 = 400 - [tex]\frac{400}{3}[/tex]

r^2 = [tex]\frac{800}{3}[/tex]

r = [tex]\frac{20\sqrt{2}}{\sqrt{3}}[/tex] or 16.33

Now, we can get maximum volume of cone.

V = 1/3[tex]\pi[/tex] *  16.33^2 * 11.55

V = 1,026.67[tex]\pi[/tex]

Thus, the radius of the cone is 16.33, the height of the cone is 11.55, and the maximum volume of the cone is 1,026.67[tex]\pi[/tex].

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