SAT Math : Solid Geometry

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #5 : How To Find The Volume Of A Sphere

At x = 3, the line y = 4x + 12 intersects the surface of a sphere that passes through the xy-plane. The sphere is centered at the point at which the line passes through the x-axis. What is the volume, in cubic units, of the sphere?

Possible Answers:

4896π√(17)

None of the other answers

2040π√(7)

816π√(11)

4896π

Correct answer:

4896π√(17)

Explanation:

We need to ascertain two values: The center point and the point of intersection with the surface.  Let's do that first:

The center is defined by the x-intercept. To find that, set the line equation equal to 0 (= 0 at the x-intercept):

0 = 4x + 12; 4x = –12; x = –3; Therefore, the center is at (–3,0)

Next, we need to find the point at which the line intersects with the sphere's surface. To do this, solve for the point with x-coordinate at 3:

y = 4 * 3 + 12; y = 12 + 12; y = 24; therefore, the point of intersection is at (3,24)

 

Reviewing our data so far, this means that the radius of the sphere runs from the center, (–3,0), to the edge, (3,24).  If we find the distance between these two points, we can ascertain the length of the radius.  From that, we will be able to calculate the volume of the sphere.

The distance between these two points is defined by the distance formula:

d = √( (x1 – x0)2 + (y1 – y0))

For our data, that is:

√( (3 + 3)2 + (24 – 0)) = √( 62 + 24)  = √(36 + 576) = √612 = √(2 * 2 * 3 * 3 * 17) = 6√(17)

Now, the volume of a sphere is defined by: V = (4/3)πr3

For our data, that would be:  (4/3)π * (6√(17))3 = (4/3) * 63 * 17√(17) * π = 4 * 2 * 62 * 17√(17) * π = 4896π√(17)

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

The surface area of a sphere is 676π in2.  How many cubic inches is the volume of the same sphere?

Possible Answers:

(2028π)/3

(8788π)/3

(2197π)/3

2028π

8788π

Correct answer:

(8788π)/3

Explanation:

To begin, we must solve for the radius of our sphere.  To do this, recall the equation for the surface area of a sphere: A = 4πr2

For our data, that is: 676π = 4πr2; 169 = r2; r = 13

From this, it is easy to solve for the volume of the sphere.  Recall the equation:

V = (4/3)πr3

For our data, this is: V = (4/3)π * 133 = (4π * 2197)/3 = (8788π)/3

Example Question #7 : How To Find The Volume Of A Sphere

What is the difference between the volume and surface area of a sphere with a radius of 6?

Possible Answers:

216π

133π

720π

288π

144π

Correct answer:

144π

Explanation:

Surface Area = 4πr2 = 4 * π * 62 = 144π

Volume = 4πr3/3 = 4 * π * 63 / 3 = 288π

Volume – Surface Area = 288π – 144π = 144π

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

A sphere is perfectly contained within a cube that has a volume of 216 units. What is the volume of the sphere?

Possible Answers:

Correct answer:

Explanation:

To begin, we must determine the dimensions of the cube. This is done by solving the simple equation:

We know the volume is 216, allowing us to solve for the length of a side of the cube.

Taking the cube root of both sides, we get s = 6.

The diameter of the sphere will be equal to side of the cube, since the question states that the sphere is perfectly contained. The diameter of the sphere will be 6, and the radius will be 3.

We can plug this into the equation for volume of a sphere:

We can cancel out the 3 in the denominator.

Simplify.

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

The surface area of a sphere is . Find the volume of the sphere in cubic millimeters.

Possible Answers:

Correct answer:

Explanation:

Example Question #111 : Solid Geometry

A solid hemisphere has a radius of length r. Let S be the number of square units, in terms of r, of the hemisphere's surface area. Let V be the number of cubic units, in terms of r, of the hemisphere's volume. What is the ratio of S to V?

Possible Answers:

\frac{9}{2r}

3r

\frac{4r}{3}

\frac{9r}{2}

\frac{3}{r}

Correct answer:

\frac{9}{2r}

Explanation:

First, let's find the surface area of the hemisphere. Because the hemisphere is basically a full sphere cut in half, we need to find half of the surface area of a full sphere. However, because the hemisphere also has a circular base, we must then add the area of the base.

S = \frac{1}{2}\cdot (surface area of sphere) + (surface area of base)

The surface area of a sphere with radius r is equal to 4\pi r^2. The surface area of the base is just equal to the surface area of a circle, which is \pi r^2.

S=\frac{1}{2}\cdot 4\pi r^2+\pi r^2=2\pi r^2+\pi r^2=3\pi r^2

The volume of the hemisphere is going to be half of the volume of an entire sphere. The volume for a full sphere is \frac{4}{3}\pi r^3.

V = \frac{1}{2}\cdot (volume of sphere)

V = \frac{1}{2}\cdot \frac{4}{3}\pi r^3=\frac{2}{3}\pi r^3

Ultimately, the question asks us to find the ratio of S to V. To do this, we can write S to V as a fraction.

\frac{S}{V}=\frac{3\pi r^2}{\frac{2}{3}\pi r^3}

In order to simplify this, let's multiply the numerator and denominator both by 3.

\frac{S}{V}=\frac{3\pi r^2}{\frac{2}{3}\pi r^3} = \frac{9\pi r^2}{2\pi r^3}=\frac{9}{2r}

The answer is \frac{9}{2r}.

Example Question #34 : Spheres

Find the volume of a sphere with a radius of .

Possible Answers:

Correct answer:

Explanation:

Write the formula to find the volume of the sphere.

Substitute the radius and solve for the volume.

Example Question #32 : Spheres

Six spheres have volumes that form an arithmetic sequence. The two smallest spheres have radii 4 and 6. Give the volume of the largest sphere.

Possible Answers:

Correct answer:

Explanation:

The volume of a sphere with radius  can be determined using the formula

.

The smallest sphere, with radius , has volume

.

The second-smallest sphere, with radius , has volume

.

The volumes are in an arithmetic sequence; their common difference is the difference of these two volumes, or

Since the six volumes are in an arithmetic sequence, the volume of the largest of the six spheres - that is, the sixth-smallest sphere - is

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

The radii of six spheres form an arithmetic sequence. The smallest and largest spheres have radii 10 and 30, respectively. Give the volume of the second-largest sphere.

Possible Answers:

None of the other responses gives a correct answer.

Correct answer:

Explanation:

The radii of the spheres form an arithmetic sequence, with 

 and 

The common difference  can be computed as follows:

The second-largest - or fifth-smallest - sphere has radius:

 

The volume of a sphere with radius  can be determined using the formula

.

Set :

Example Question #15 : How To Find The Volume Of A Sphere

A sphere with radius  fits perfectly inside of a cube so that the sides of the cube are barely touching the sphere. What is the volume of the cube that is not occupied by the sphere? 

Possible Answers:

Correct answer:

Explanation:

Because the sides of the interior of the cube are tangent to the sphere, we know that the length of each side is equal to the diameter of the sphere. Since the radius of this sphere is , then its diameter is

To find the volume that is not occupied by the sphere, we will subtract the sphere's volume from the volume of the cube.

The volume of the cube is: 

The volume of the sphere is:

Therefore, with these values, the volume of the cube not occupied by the sphere is:

 

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