Advanced Geometry : Solid Geometry

Study concepts, example questions & explanations for Advanced Geometry

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Example Questions

Example Question #21 : Solid Geometry

The circumference of the base of a cone is 100; the height of the cone is equal to the diameter of the base. Give the surface area of the cone (nearest whole number).

Possible Answers:

\(\displaystyle 2,575\)

\(\displaystyle 8,443\)

\(\displaystyle 1,589\)

\(\displaystyle 1,779\)

\(\displaystyle 2,385\)

Correct answer:

\(\displaystyle 2,575\)

Explanation:

The formula for the surface area of a cone with base of radius \(\displaystyle r\) and slant height \(\displaystyle l\) is

\(\displaystyle A = \pi r^{2} + \pi r l\).

The diameter of the base is the circumference divided by \(\displaystyle \pi\), which is 

\(\displaystyle d = C \div (2\pi ) \approx 100 \div 3.14 \approx 31.83\)

This is also the height \(\displaystyle h\).

The radius is half this, or 

\(\displaystyle r = d \div 2 \approx 31.83 \div 2 \approx 15.92\)

The slant height can be found by way of the Pythagorean Theorem:

\(\displaystyle l = \sqrt{r^{2}+ h ^{2}}\)

\(\displaystyle l \approx \sqrt{15.92^{2}+ 31.83 ^{2}}\)

\(\displaystyle l \approx \sqrt{253.30+ 1,013.21}\)

\(\displaystyle l \approx \sqrt{1266.51}\)

\(\displaystyle l \approx 35.60\)

Substitute in the surface area formula:

\(\displaystyle A = \pi r^{2} + \pi r l\)

\(\displaystyle A \approx 3.14 \cdot 15.92 ^{2} + 3.14 \cdot 15.92 \cdot 35.60\)

\(\displaystyle A \approx 795.8+ 1,780.1\)

\(\displaystyle A \approx 2,575\)

Example Question #21 : Cones

If a cone were unfurled into a 2-dimensional figure. The lateral area of the cone would look most like which figure? 

Possible Answers:

Rectangle

Circle

Sector of a Circle

Triangle

Correct answer:

Sector of a Circle

Explanation:

When creating a net image of a 3D figure - one imagines it is made of paper and is unfurled into its' 2D form. The lateral portion of the cone cone would be unfurled into the image of a Sector of a Circle. To include the full surface area of the cone a circle is included to form the base of the cone as in the figure below. The lateral area portion is the top part of the figure below. 

Cone net

Example Question #23 : Solid Geometry

As shown by the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

1

Possible Answers:

\(\displaystyle 2635.09\)

\(\displaystyle 2155.13\)

\(\displaystyle 2335.69\)

\(\displaystyle 2274.11\)

Correct answer:

\(\displaystyle 2155.13\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(15)(14)\pi=210\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(14)(10)+\pi(14)^2=476\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=210\pi+476\pi=686\pi=2155.13\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #24 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

2

Possible Answers:

\(\displaystyle 1745.68\)

\(\displaystyle 1966.37\)

\(\displaystyle 1809.56\)

\(\displaystyle 1817.24\)

Correct answer:

\(\displaystyle 1809.56\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(20)(12)\pi=240\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(12)(8)+\pi(12)^2=336\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=240\pi+336\pi=576\pi=1809.56\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #25 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

 

3

Possible Answers:

\(\displaystyle 196.35\)

\(\displaystyle 258.43\)

\(\displaystyle 208.09\)

\(\displaystyle 201.06\)

Correct answer:

\(\displaystyle 201.06\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(8)(4)\pi=32\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(4)(2)+\pi(4)^2=32\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=32\pi+32\pi=64\pi=201.06\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #26 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

4

Possible Answers:

\(\displaystyle 581.74\)

\(\displaystyle 565.49\)

\(\displaystyle 509.31\)

\(\displaystyle 652.22\)

Correct answer:

\(\displaystyle 565.49\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(13)(5)\pi=65\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(5)(9)+\pi(5)^2=115\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=65\pi+115\pi=180\pi=565.49\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #27 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

5

Possible Answers:

\(\displaystyle 398.32\)

\(\displaystyle 411.22\)

\(\displaystyle 389.56\)

\(\displaystyle 376.09\)

Correct answer:

\(\displaystyle 389.56\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(15)(4)\pi=60\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(4)(6)+\pi(4)^2=64\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=60\pi+64\pi=124\pi=389.56\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #28 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

6

Possible Answers:

\(\displaystyle 353.08\)

\(\displaystyle 410.58\)

\(\displaystyle 374.19\)

\(\displaystyle 389.56\)

Correct answer:

\(\displaystyle 389.56\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(9)(4)\pi=36\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(9)(4)+\pi(4)^2=88\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=36\pi+88\pi=124\pi=389.56\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #29 : Solid Geometry

In the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

7

Possible Answers:

\(\displaystyle 1309.67\)

\(\displaystyle 1288.05\)

\(\displaystyle 1316.59\)

\(\displaystyle 1244.32\)

Correct answer:

\(\displaystyle 1288.05\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(15)(10)\pi=150\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(10)(8)+\pi(10)^2=260\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=150\pi+260\pi=410\pi=1288.05\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #21 : Cones

As shown by the figure below, a cone is placed on top of a cylinder so that they share the same base. Find the surface area of the figure.

9

Possible Answers:

\(\displaystyle 1492.19\)

\(\displaystyle 1476.55\)

\(\displaystyle 1509.20\)

\(\displaystyle 1341.61\)

Correct answer:

\(\displaystyle 1476.55\)

Explanation:

13

First, find the lateral surface area of the cone.

\(\displaystyle \text{Lateral Surface Area}=(\text{slant height})(\pi)(\text{radius})\)

Plug in the given slant height and radius.

\(\displaystyle \text{Lateral Area}=(13)(10)\pi=130\pi\)

Next, find the surface area of the cylinder:

\(\displaystyle \text{Surface Area of Cylinder}=2\pi(\text{radius})(\text{height})+2\pi(\text{radius})^2\)

The surface area of the cylinder is the sum of the lateral surface area of the cylinder and its two bases. However, since one base of the cylinder is covered up by the cone, we will need to subtract that area out of the total surface area of the cylinder.

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(\text{radius})(\text{height})+\pi(\text{radius})^2\)

Plug in the given height and radius to find the surface area of the cylindrical portion of the figure:

\(\displaystyle \text{Surface Area of Cylindrical Portion}=2\pi(10)(12)+\pi(10)^2=340\pi\)

To find the surface area of the figure, add together the lateral area of the cone with the surface area of the cylindrical portion of the figure.

\(\displaystyle \text{Surface Area of Figure}=130\pi+340\pi=470\pi=1476.55\)

Make sure to round to \(\displaystyle 2\) places after the decimal.

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