ACT Math : How to find the volume of a sphere

Study concepts, example questions & explanations for ACT Math

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Example Questions

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

For a sphere the volume is given by = (4/3)πr3 and the surface area is given by = 4πr2. If the sphere has a surface area of 256π, what is the volume?

Possible Answers:

750π

300π

615π

683π

Correct answer:

683π

Explanation:

Given the surface area, we can solve for the radius and then solve for the volume.

4πr2 = 256π

4r2 = 256

r2 = 64

r = 8

Now solve the volume equation, substituting for r:

V = (4/3)π(8)3

V = (4/3)π*512

V = (2048/3)π

V = 683π

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

The specifications of an official NBA basketball are that it must be 29.5 inches in circumference and weigh 22 ounces.  What is the approximate volume of the basketball?   Remember that the volume of a sphere is calculated by V=(4πr3)/3

 

Possible Answers:

434.19 cu.in.

138.43 cu.in.

92.48 cu.in.

3468.05 cu.in.

8557.46 cu.in.

Correct answer:

434.19 cu.in.

Explanation:

To find your answer, we would use the formula:  C=2πr. We are given that C = 29.5. Thus we can plug in to get  [29.5]=2πr and then multiply 2π to get 29.5=(6.28)r.  Lastly, we divide both sides by 6.28 to get 4.70=r. Then we would plug into the formula for volume V=(4π〖(4.7)〗3) / 3   (The information given of 22 ounces is useless) 

 

 

 

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

The radius of a sphere is \(\displaystyle 6\). What is the approximate volume of this sphere?

Possible Answers:

516\pi\(\displaystyle 516\pi\)

300\pi\(\displaystyle 300\pi\)

20\pi\(\displaystyle 20\pi\)

288\pi\(\displaystyle 288\pi\)

138\pi\(\displaystyle 138\pi\)

Correct answer:

288\pi\(\displaystyle 288\pi\)

Explanation:

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

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

\(\displaystyle V=\frac{4}{3}\pi(216)\)

\(\displaystyle V=288\pi\)

Example Question #2 : How To Find The Volume Of A Sphere

A cube has a side dimension of 4. A sphere has a radius of 3. What is the volume of the two combined, if the cube is balanced on top of the sphere?

Possible Answers:

\(\displaystyle 16 + 36\pi\)

\(\displaystyle 64 + 6\pi\)

\(\displaystyle 16 + 6\pi\)

\(\displaystyle 4 + 36\pi\)

\(\displaystyle 64 + 36\pi\)

Correct answer:

\(\displaystyle 64 + 36\pi\)

Explanation:

\(\displaystyle V_{cube}=(\text{side})^3=(4)^3=64\)

\(\displaystyle V_{sphere}=\frac{4}{3}\pi r^3=\frac{4}{3}\pi(3^3)=\frac{4}{3}\pi(27)=36\pi\)

\(\displaystyle V_{total}=64+36\pi\)

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

What is the volume of a sphere with a diameter of 6 in?

Possible Answers:

\(\displaystyle 108\pi\ in^{3}\)

\(\displaystyle 288\pi\ in^{3}\)

\(\displaystyle 216\pi\ in^{3}\)

\(\displaystyle 36\pi\ in^{3}\)

\(\displaystyle 72\pi\ in^{3}\)

Correct answer:

\(\displaystyle 36\pi\ in^{3}\)

Explanation:

The formula for the volume of a sphere is:

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

where \(\displaystyle r\) = radius.  The diameter is 6 in, so the radius will be 3 in. 

Example Question #672 : Geometry

If the diameter of a sphere is \(\displaystyle 10\), find the approximate volume of the sphere?

Possible Answers:

\(\displaystyle 334\pi\)

\(\displaystyle 167\pi\)

\(\displaystyle 143\pi\)

\(\displaystyle 95\pi\)

\(\displaystyle 205\pi\)

Correct answer:

\(\displaystyle 167\pi\)

Explanation:

The volume of a sphere = \(\displaystyle \frac{4}{3}\pi r^{3}\)

Radius is \(\displaystyle \frac{1}{2}\) of the diameter so the radius = 5.

\(\displaystyle V=\frac{4}{3}\pi5^{3}\)

or \(\displaystyle V=\frac{500}{3\pi}\)

which is approximately \(\displaystyle 167\pi\)

Example Question #1021 : Act Math

What is the volume of a sphere with a diameter of \(\displaystyle 12\) inches? Leave your answer in terms of \(\displaystyle \pi\).

Possible Answers:

\(\displaystyle 36\pi in^3\)

\(\displaystyle 2404\pi in^3\)

\(\displaystyle 576\pi in^3\)

\(\displaystyle 288\pi in^2\)

\(\displaystyle 288\pi in^3\)

Correct answer:

\(\displaystyle 288\pi in^3\)

Explanation:

To find the volume of a sphere we use the sphere volume formula:

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

First we need to find the radius of the sphere. A sphere has a radius of half the diameter. So we see that \(\displaystyle 12/2 =6=r\).

Next we plug 6 in for our radius and get
\(\displaystyle V = \frac{4}{3}\pi 6^3=288\pi in^3\) 

(don't forget your units).

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

What is the volume of a sphere with a diameter of \(\displaystyle \textup{6 inches}\) (reduce all fractions)?

Possible Answers:

\(\displaystyle \frac{864}{3}\pi\textup{ in}^3\)

\(\displaystyle 108\pi\textup{ in}^3\)

\(\displaystyle \frac{108}{3}\pi\textup{ in}^3\)

\(\displaystyle 36\pi\textup{ in}^3\)

\(\displaystyle 144\pi\textup{ in}^3\)

Correct answer:

\(\displaystyle \frac{108}{3}\pi\textup{ in}^3\)

Explanation:

The formula for the volume of a sphere is:
\(\displaystyle v = \frac{4}{3}\pi * r^3\), thus we need to just determine the radius and plug it into the equation. Remember that \(\displaystyle 2r = d\) and so 

\(\displaystyle 6 = 2r \newline 3 = r\)

And plugging in we get \(\displaystyle \frac{108}{3}\pi \textup{in}^3\)

Example Question #2 : How To Find The Volume Of A Sphere

What is the volume of a sphere with a surface area of \(\displaystyle 576\pi\textup{ ft}^2\)? (Simplify all fractions in your answer.)

Possible Answers:

\(\displaystyle 2304 \pi\textup{ ft}^3\)

\(\displaystyle 2304 \pi\textup{ ft}^2\)

\(\displaystyle 2304\pi\textup{ ft}^3\)

\(\displaystyle 18432\pi\textup{ ft}^3\)

\(\displaystyle 288\pi\textup{ ft}^3\)

Correct answer:

\(\displaystyle 2304\pi\textup{ ft}^3\)

Explanation:

First find the radius from the surface area set the given surface area equal to the surface area formula and solve for the radius.
\(\displaystyle 576\pi = 4\pi r^2\)

\(\displaystyle 144\pi = \pi r^2 \newline 144 = r^2 \newline 12 = r\)

Now plug the radius into the volume formula:
\(\displaystyle V = \frac{4}{3}\pi r^3 = \frac{4}{3}\pi 12^3 = 2304 \pi\textup{ ft}^3\)

Example Question #6 : How To Find The Volume Of A Sphere

If Ariana’s orange has twice the radius of Autumn’s orange, the volume of Ariana’s orange is how many times larger than the volume of Autumn’s orange?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 6\)

\(\displaystyle 10\)

\(\displaystyle 2\)

\(\displaystyle 8\)

Correct answer:

\(\displaystyle 8\)

Explanation:

Define the radius of Autumn’s orange as r. The volume of her orange is \(\displaystyle \pi r^3\). Ariana’s orange has twice the radius of Autumn’s, so the radius of her orange is \(\displaystyle 2r\), and the volume is \(\displaystyle \pi(2r)^3 = 8\pi r^3\), which is 8 times larger than Autumn’s orange.

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