High School Math : Cones

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Cones

What is the volume of a cone with a height of \(\displaystyle 9\) and a base with a radius of \(\displaystyle 13\)?

Possible Answers:

\(\displaystyle 117\pi\)

\(\displaystyle 396\pi\)

\(\displaystyle 507\pi\)

\(\displaystyle 1521\pi\)

Correct answer:

\(\displaystyle 507\pi\)

Explanation:

To find the volume of a cone we must use the equation \(\displaystyle V=\frac{1}{3}(A_{base})(H)\). In this formula, \(\displaystyle A_{base}\) is the area of the circular base of the cone, and \(\displaystyle H\) is the height of the cone.

We must first solve for the area of the base using \(\displaystyle r=13\).

The equation for the area of a circle is \(\displaystyle A=\pi(r^{2})\). Using this, we can adjust our formula and plug in the value of our radius.

\(\displaystyle V=\frac{1}{3}(A_{base})(H)=\frac{1}{3}(\pi r^2)(H)=\frac{1}{3}(\pi (13)^2)(H)\)

\(\displaystyle 13^2=169\)

\(\displaystyle V=\frac{1}{3}(169\pi)(H)\)

Now we can plug in our given height, \(\displaystyle H=9\).

\(\displaystyle V=\frac{1}{3}(169\pi)(9)\)

Multiply everything out to solve for the volume.

\(\displaystyle V=\frac{1}{3}(169\pi)(9)=(169\pi)(3)=507\pi\)

The volume of the cone is \(\displaystyle 507\pi\).

Example Question #1 : Solid Geometry

What is the equation of a circle with a center of (5,15) and a radius of 7?

Possible Answers:

\(\displaystyle (x-5)^2+(y-15)^2=7\)

\(\displaystyle (x-5)^2+(y-15)^2=14\)

\(\displaystyle (x+5)^2+(y+15)^2=49\)

\(\displaystyle (x-5)^2+(y-15)^2=49\)

Correct answer:

\(\displaystyle (x-5)^2+(y-15)^2=49\)

Explanation:

To find the equation of a circle we must first know the standard form of the equation of a circle which is

The letters \(\displaystyle h\) and \(\displaystyle k\) represent the \(\displaystyle x\)-value and \(\displaystyle y\)-value of the center of the circle respectively.

In this case \(\displaystyle h\) is 5 and k is 15 so plugging the values into the equation yields \(\displaystyle (x-5)^2+(y-15)^2=r^2\)

We then plug the radius into the equation to get \(\displaystyle (x-5)^2+(y-15)^2=7^2\)

Square it to yield \(\displaystyle (x-5)^2+(y-15)^2=49\)

The equation with a center of (5,15) and a radius of 7 is \(\displaystyle (x-5)^2+(y-15)^2=49\).

 

Example Question #1 : How To Find The Volume Of A Cone

\(\displaystyle \textup{Find the volume, to the nearest cubic inch, of a cone with a radius of 8 inches}\)

\(\displaystyle \textup{at its base and a height of one foot.}\)

Possible Answers:

\(\displaystyle 2413\)

\(\displaystyle 67\)

\(\displaystyle 1206\)

\(\displaystyle 302\)

\(\displaystyle 804\)

Correct answer:

\(\displaystyle 804\)

Explanation:

\(\displaystyle V= \frac{1}{3} \pi r^{2}h\;\;\textup{Given: }r=8\textup{ inches}, h=12\textup{ inches}\)

\(\displaystyle V = \frac{1}{3} \pi\times8^{2}\times12\;\;\;\;\;V = 256\pi\;\;\;V=804.2\)

Example Question #1 : How To Find The Volume Of A Cone

What is the volume of a cone that has a radius of 3 and a height of 4?

Possible Answers:

\(\displaystyle 12\pi\)

\(\displaystyle 36\pi\)

\(\displaystyle 12\pi\)

\(\displaystyle 9\pi\)

\(\displaystyle 4\pi\)

Correct answer:

\(\displaystyle 12\pi\)

Explanation:

The standard equation for the volume of a cone is 

\(\displaystyle v=\frac{1}{3}\pi (r)^2h\)

where \(\displaystyle r\) denotes the radius and \(\displaystyle h\) denotes the height. 

Plug in the given values for \(\displaystyle r\) and \(\displaystyle h\) to find the answer:

\(\displaystyle v=\frac{1}{3}\pi (3)^2(4)=\frac{1}{3}\pi (9)(4)=12\pi\)

Example Question #1 : Cones

Find the volume of the following cone.

Cone

Possible Answers:

\(\displaystyle 70 \pi m^3\)

\(\displaystyle 100 \pi m^3\)

\(\displaystyle 130 \pi m^3\)

\(\displaystyle 115 \pi m^3\)

\(\displaystyle 85 \pi m^3\)

Correct answer:

\(\displaystyle 100 \pi m^3\)

Explanation:

The formula for the volume of a cone is:

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

where \(\displaystyle r\) is the radius of the cone and \(\displaystyle h\) is the height of the cone.

 

In order to find the height of the cone, use the Pythagorean Theorem:

\(\displaystyle A^2 + B^2 = C^2\)

\(\displaystyle A^2 + (5m)^2 = (13m)^2\)

\(\displaystyle A^2 = 144m^2\)

\(\displaystyle A = 12m\)

 

Plugging in our values, we get:

\(\displaystyle V= \frac{\pi (5m)^2 (12m)}{3}\)

\(\displaystyle V= \pi (25m^2)(4m)=100 \pi m^3\)

Example Question #1 : Cones

Find the volume of the following cone.

Cone

Possible Answers:

\(\displaystyle 86 \pi m^3\)

\(\displaystyle 106 \pi m^3\)

\(\displaystyle 76 \pi m^3\)

\(\displaystyle 96 \pi m^3\)

\(\displaystyle 116 \pi m^3\)

Correct answer:

\(\displaystyle 96 \pi m^3\)

Explanation:

The formula for the volume of a cone is:

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

Where \(\displaystyle r\) is the radius of the cone and \(\displaystyle h\) is the height of the cone

 

Use the Pythagorean Theorem to find the length of the radius:

\(\displaystyle A^2 + B^2 = C^2\)

\(\displaystyle A^2 + (8m)^2 = (10m)^2\)

\(\displaystyle A = 6m\)

 

Plugging in our values, we get:

\(\displaystyle V = \frac{\pi (6m)^2 8m}{3}\)

\(\displaystyle V = 96 \pi m^3\)

Example Question #1 : Cones

Find the volume of the following half cone.

Half_cone

Possible Answers:

\(\displaystyle 140 \pi m^3\)

\(\displaystyle 170 \pi m^3\)

\(\displaystyle 150 \pi m^3\)

\(\displaystyle 160 \pi m^3\)

\(\displaystyle 180 \pi m^3\)

Correct answer:

\(\displaystyle 160 \pi m^3\)

Explanation:

The formula of the volume of a half cone is:

\(\displaystyle V=\frac{1}{3}(base)(height)\)

\(\displaystyle V = \frac{1}{3}\left(\frac{1}{2}\pi r^2\right)(h)\)

Where \(\displaystyle r\) is the radius of the cone and \(\displaystyle h\) is the height of the cone.

 

Use the Pythagorean Theorem to find the height of the cone:

\(\displaystyle A^2+B^2 = C^2\)

\(\displaystyle A^2+(8m)^2=(17m)^2\)

\(\displaystyle A=15m\)

 

\(\displaystyle V = \frac{1}{3}\left(\frac{1}{2}\pi (8m)^2\right)(15m)\)

\(\displaystyle V=160 \pi m^3\)

Example Question #1 : Solid Geometry

What is the volume of a right cone with a diameter of 6 cm and a height of 5 cm?

Possible Answers:

\(\displaystyle 60\pi \ cm^{3}\)

\(\displaystyle 15\pi \ cm^{3}\)

\(\displaystyle 120\pi \ cm^{3}\)

\(\displaystyle 45\pi \ cm^{3}\)

\(\displaystyle 180\pi \ cm^{3}\)

Correct answer:

\(\displaystyle 15\pi \ cm^{3}\)

Explanation:

The general formula is given by V = 1/3Bh = 1/3\pi r^{2}h\(\displaystyle V = 1/3Bh = 1/3\pi r^{2}h\), where \(\displaystyle r\) = radius and \(\displaystyle h\) = height.

The diameter is 6 cm, so the radius is 3 cm.

\(\displaystyle V=\frac{\pi 3^2\times 5}{3}=15\pi\)

Example Question #1 : Solid Geometry

There is a large cone with a radius of 4 meters and height of 18 meters. You can fill the cone with water at a rate of 3 cubic meters every 25 seconds. How long will it take you to fill the cone?

Possible Answers:

\(\displaystyle 600\ \textup{minutes}\)

\(\displaystyle 800\ \textup{minutes}\)

\(\displaystyle 3\ \textup{minutes}\ 20\ \textup{seconds}\)

 

\(\displaystyle 60\ \textup{minutes}\)

\(\displaystyle 41\ \textup{minutes}\ 53\ \textup{seconds}\)

Correct answer:

\(\displaystyle 41\ \textup{minutes}\ 53\ \textup{seconds}\)

Explanation:

First we will calculate the volume of the cone

\(\displaystyle V=\frac{1}{3}\pi r^{2}h=\frac{1}{3}\pi\cdot 4^{2}\cdot 18=96\pi\ m^{3}\)

Next we will determine the time it will take to fill that volume

\(\displaystyle 96\pi \ m^{3}\times \frac{25\ s}{3\ m^{3}}=800\pi \ s\)

We will then convert that into minutes

\(\displaystyle 800\pi \ s\times \frac{1\ minute}{60\ seconds}=13.\overline{3}\pi \ minutes\approx 41.9\ minutes\approx 41\ minutes\ 53\ seconds\)

Example Question #3 : How To Find The Volume Of A Cone

You have an empty cylinder with a base diameter of 6 and a height of 10 and you have a cone full of water with a base radius of 3 and a height of 10.  If you empty the cone of water into the cylinder, how much volume is left empty in the cylinder?

Possible Answers:

\(\displaystyle 30\pi\)

\(\displaystyle 45\pi\)

\(\displaystyle 90\pi\)

\(\displaystyle 60\pi\)

\(\displaystyle 120\pi\)

Correct answer:

\(\displaystyle 60\pi\)

Explanation:

Cylinder Volume = \(\displaystyle \pi*r^{2}*h\)

Cone Volume = \(\displaystyle \frac{1}{3}*\pi*r^{2}*h\)

Cylinder Diameter = 6, therefore Cylinder Radius = 3

Cone Radius = 3

Empty Volume = Cylinder Volume – Cone Volume

\(\displaystyle =\pi*r^{2}*h-\frac{1}{3}*\pi*r^{2}*h\) 

\(\displaystyle =\pi*3^{2}*10-\frac{1}{3}*\pi*3^{2}*10\)

\(\displaystyle =\pi*90-\pi*30\)

\(\displaystyle =\pi*60\)

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