Question 438345
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You asked how many "square feet" lie in the void.  The only way that makes any sense is if you are asking about the total surface area of the cylinder-shaped void.


The Total Surface Area of a cylinder is given by the sum of the areas of the two circular bases plus the lateral surface area which is given by the circumference of one of the bases times the height of the cylinder (making sure to normalize the units).


The area of one of the bases is *[tex \Large \pi] times the square of the radius of the circle.  We are given the circumference which is equal to 2 times *[tex \Large \pi] times the radius -- hence the radius is the circumference divided by *[tex \Large 2\pi].


Area of the two circular bases:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ A_{bases}\ =\ 2\,\cdot\,A_{base}\ =\ 2\,\cdot\,\pi\,\cdot\,\left(\frac{370}{2\pi}\right)^2\ =\ \frac{370^2}{2\pi}]


Lateral area:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ A_{lateral}\ =\ \frac{370}{3}]


because 4" is *[tex \Large \frac{1}{3}\ \ ]foot.


Hence the total surface area is


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{370^2}{2\pi}\ +\ \frac{370}{3}\ \ \text{ft^2}]


You can run a calculator as well as I can to complete the arithmetic.


On the other hand, if what you <i>really</i> meant was "cubic feet" meaning you wanted the volume of removed material, that is another thing altogether.


The volume of a cylinder is the area of one of the bases times the height.


Take the area of the two bases from above and divide by 2.  Then multiply by the 1/3 foot height.


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{370^2}{4\pi}\ \cdot\ \frac{1}{3}\ =\ \frac{370^2}{12\pi}\ \ \text{ft^3}]



John
*[tex \LARGE e^{i\pi} + 1 = 0]
My calculator said it, I believe it, that settles it
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