Intermediate Geometry : Solid Geometry

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #11 : How To Find The Surface Area Of A Sphere

Find the surface area of a hemisphere with a radius of \(\displaystyle 8\).

Possible Answers:

\(\displaystyle 623.35\)

\(\displaystyle 603.19\)

\(\displaystyle 625.88\)

\(\displaystyle 608.08\)

Correct answer:

\(\displaystyle 603.19\)

Explanation:

13

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

\(\displaystyle \text{Surface Area of Sphere}=4\pi r^2\), where \(\displaystyle r\) is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

\(\displaystyle \text{Area of Circle}=\pi r^2\)

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

\(\displaystyle \text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2\)

Plug in the given radius to find the surface area.

\(\displaystyle \text{Surface Area of Hemisphere}=3\pi (8)^2=603.19\)

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

Example Question #52 : Spheres

Find the surface area of a hemisphere with a radius of \(\displaystyle 10\).

Possible Answers:

\(\displaystyle 942.48\)

\(\displaystyle 958.87\)

\(\displaystyle 905.67\)

\(\displaystyle 933.62\)

Correct answer:

\(\displaystyle 942.48\)

Explanation:

13

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

\(\displaystyle \text{Surface Area of Sphere}=4\pi r^2\), where \(\displaystyle r\) is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

\(\displaystyle \text{Area of Circle}=\pi r^2\)

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

\(\displaystyle \text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2\)

Plug in the given radius to find the surface area.

\(\displaystyle \text{Surface Area of Hemisphere}=3\pi (10)^2=942.48\)

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

Example Question #55 : Spheres

Find the surface area of a hemisphere with a radius of \(\displaystyle 11\).

Possible Answers:

\(\displaystyle 1258.25\)

\(\displaystyle 1000.27\)

\(\displaystyle 1323.98\)

\(\displaystyle 1140.40\)

Correct answer:

\(\displaystyle 1140.40\)

Explanation:

13

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

\(\displaystyle \text{Surface Area of Sphere}=4\pi r^2\), where \(\displaystyle r\) is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

\(\displaystyle \text{Area of Circle}=\pi r^2\)

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

\(\displaystyle \text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2\)

Plug in the given radius to find the surface area.

\(\displaystyle \text{Surface Area of Hemisphere}=3\pi (11)^2=1140.40\)

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

Example Question #53 : Spheres

Find the surface area of a hemisphere that has a radius of \(\displaystyle \frac{1}{4}\).

Possible Answers:

\(\displaystyle 0.81\)

\(\displaystyle 0.59\)

\(\displaystyle 0.58\)

\(\displaystyle 0.67\)

Correct answer:

\(\displaystyle 0.59\)

Explanation:

13

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

\(\displaystyle \text{Surface Area of Sphere}=4\pi r^2\), where \(\displaystyle r\) is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

\(\displaystyle \text{Area of Circle}=\pi r^2\)

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

\(\displaystyle \text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2\)

Plug in the given radius to find the surface area.

\(\displaystyle \text{Surface Area of Hemisphere}=3\pi (\frac{1}{4})^2=0.59\)

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

Example Question #12 : How To Find The Surface Area Of A Sphere

Find the surface area of a hemisphere that has a radius of \(\displaystyle \frac{3}{2}\).

Possible Answers:

\(\displaystyle 24.84\)

\(\displaystyle 21.21\)

\(\displaystyle 20.59\)

\(\displaystyle 23.23\)

Correct answer:

\(\displaystyle 21.21\)

Explanation:

13

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

\(\displaystyle \text{Surface Area of Sphere}=4\pi r^2\), where \(\displaystyle r\) is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

\(\displaystyle \text{Area of Circle}=\pi r^2\)

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

\(\displaystyle \text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2\)

Plug in the given radius to find the surface area.

\(\displaystyle \text{Surface Area of Hemisphere}=3\pi (\frac{3}{2})^2=21.21\)

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

Example Question #291 : Solid Geometry

True or false: A sphere with radius 1 has surface area \(\displaystyle 3 \pi\).

Possible Answers:

False

True

Correct answer:

False

Explanation:

Given radius \(\displaystyle r\), the surface area of a sphere \(\displaystyle A\) can be calculated according to the formula

\(\displaystyle A = 4 \pi r ^{2}\)

Set \(\displaystyle r = 1\):

\(\displaystyle A = 4 \pi \cdot 1 ^{2} = 4 \pi \cdot 1 = 4 \pi\)

The statement is false.

Example Question #1 : How To Find The Diameter Of A Sphere

The surface area of a sphere is \(\displaystyle 100\pi \; in^{2}\).  What is the diameter of the sphere?

Possible Answers:

\(\displaystyle 20\; in\)

\(\displaystyle 15\; in\)

\(\displaystyle 10\; in\)

\(\displaystyle 5\; in\)

Correct answer:

\(\displaystyle 10\; in\)

Explanation:

The surface area of a sphere is given by \(\displaystyle SA=4\pi r^{2}\)

So the equation to sovle becomes \(\displaystyle 4\pi r^{2}=100\pi\) or \(\displaystyle r^{2}=25\) so \(\displaystyle r=5\; in\)

To answer the question we need to find the diameter:

\(\displaystyle d=2r=2\cdot 5=10\; in\)

Example Question #1 : How To Find The Diameter Of A Sphere

If the volume of a sphere is \(\displaystyle 2\:units\), what is the sphere's diameter?

Possible Answers:

\(\displaystyle 2\sqrt[3]{\frac{2\pi}{3}}\)

\(\displaystyle \sqrt[3]{\frac{4\pi}{3}}\)

\(\displaystyle \sqrt[3]{\frac{2\pi}{3}}\)

\(\displaystyle \sqrt[3]{\frac{3}{2\pi}}\)

\(\displaystyle 2\sqrt[3]{\frac{3}{2\pi}}\)

Correct answer:

\(\displaystyle 2\sqrt[3]{\frac{3}{2\pi}}\)

Explanation:

Write the formula for the volume of a sphere:

\(\displaystyle V=\frac{4}{3}\pi r^3\)

Plug in the volume and find the radius by solving for \(\displaystyle r\):

\(\displaystyle 2=\frac{4}{3}\pi r^3\)

Start solving for \(\displaystyle r\) by multiplying both sides of the equation by \(\displaystyle 3\):

\(\displaystyle 2\cdot3=\frac{4}{3}\pi r^3\cdot3\)

\(\displaystyle 6=4\pi r^3\)

Now, divide each side of the equation by \(\displaystyle 4\pi\):

\(\displaystyle \frac{6}{4\pi}=\frac{4\pi r^3}{4\pi}\)

\(\displaystyle \frac{6}{4\pi}=r^3\)

Reduce the left side of the equation:

\(\displaystyle \frac{3}{2\pi}=r^3\)

Finally, take the cubed root of both sides of the equation:

\(\displaystyle \sqrt[3]{\frac{3}{2\pi}}=r\)

Keep in mind that you've solved for the radius, not the diameter. The diameter is double the radius, which is: \(\displaystyle 2\sqrt[3]{\frac{3}{2\pi}}\).

Example Question #292 : Solid Geometry

The circumference of a sphere is \(\displaystyle 84.823 \:in\). Find the radius.

Possible Answers:

\(\displaystyle 27.5\:in\)

\(\displaystyle 27.0\:in\)

\(\displaystyle 14.0\: in\)

\(\displaystyle 13.5\:in\)

\(\displaystyle 13.7\:in\)

Correct answer:

\(\displaystyle 13.5\:in\)

Explanation:

If the circumference of a sphere is \(\displaystyle 84.823 \:in\), that means we can easily solve for the diameter by using \(\displaystyle C=\pi \cdot d\). This is the equation to find the circumference. 

By substituting in the value for circumference (\(\displaystyle C\)), we can solve for the missing variable \(\displaystyle d\)

\(\displaystyle 84.823\:in= \pi \cdot d\)

\(\displaystyle \frac{84.823\:in}{ \pi}= d\)

\(\displaystyle d = 27\: in\)

To find the radius of the sphere, we need to divide this value by \(\displaystyle 2\):

\(\displaystyle r=\frac{d}{2}=\frac{27\:in}{2}=13.5\:in\)

 

Example Question #291 : Solid Geometry

Find the diameter of a sphere if the volume is \(\displaystyle \pi\).

Possible Answers:

\(\displaystyle \sqrt[3]{\frac{3}{4}}\)

\(\displaystyle 2\sqrt[3]{\frac{3}{4}}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle 1\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 2\sqrt[3]{\frac{3}{4}}\)

Explanation:

Write the formula for the volume of a sphere.

\(\displaystyle V=\frac{4}{3}\pi r^3\)

Plug in the given volume and solve for the radius.

\(\displaystyle \pi=\frac{4}{3}\pi r^3\)

\(\displaystyle \frac{3}{4}= r^3\)

\(\displaystyle r=\sqrt[3]{\frac{3}{4}}\)

The diameter is double the radius.

\(\displaystyle d=2\sqrt[3]{\frac{3}{4}}\)

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