Calculus 1 : Functions

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #28 : How To Find Volume Of A Region

Sphere segment

A sphere with a radius of 5 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 4 units to the left of the origin and the second cut is 2 units to the left of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle \frac{251}{3}\pi\)

\(\displaystyle \frac{128}{3}\pi\)

\(\displaystyle \frac{23}{3}\pi\)

\(\displaystyle \frac{94}{3}\pi\)

\(\displaystyle \frac{49}{3}\pi\)

Correct answer:

\(\displaystyle \frac{94}{3}\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(5^2x-\frac{x^3}{3})|_{-4}^{-2}\)

\(\displaystyle V=\pi(5^2(-2)-\frac{(-2)^3}{3})-\pi(5^2(-4)-\frac{(-4)^3}{3})\)

\(\displaystyle V=\frac{94}{3}\pi\)

 

Example Question #29 : How To Find Volume Of A Region

Sphere segment

A sphere with a radius of 10  has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 4 units to the left of the origin and the second cut is 3 units to the right of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle \frac{3112}{3}\pi\)

\(\displaystyle \frac{4129}{3}\pi\)

\(\displaystyle \frac{2009}{3}\pi\)

\(\displaystyle \frac{802}{3}\pi\)

\(\displaystyle \frac{1984}{3}\pi\)

Correct answer:

\(\displaystyle \frac{2009}{3}\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(10^2x-\frac{x^3}{3})|_{-4}^{3}\)

\(\displaystyle V=\pi(10^2(3)-\frac{(3)^3}{3})-\pi(10^2(-4)-\frac{(-4)^3}{3})\)

\(\displaystyle V=\frac{2009}{3}\pi\)

 

Example Question #30 : How To Find Volume Of A Region

Sphere segment

A sphere with a radius of 3 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 2 units to the left of the origin and the second cut is 1 unit to the right of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle 24\pi\)

\(\displaystyle 12\pi\)

\(\displaystyle \frac{20}{3}\pi\)

\(\displaystyle \frac{40}{3}\pi\)

\(\displaystyle 30\pi\)

Correct answer:

\(\displaystyle 24\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(3^2x-\frac{x^3}{3})|_{-2}^{1}\)

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

\(\displaystyle V=24\pi\)

 

Example Question #31 : Volume

Sphere segment

A sphere with a radius of 7 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 6 units to the left of the origin and the second cut is 5 units to the left of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle \frac{56}{3}\pi\)

\(\displaystyle \frac{29}{3}\pi\)

\(\displaystyle \frac{28}{3}\pi\)

\(\displaystyle \frac{58}{3}\pi\)

\(\displaystyle \frac{14}{3}\pi\)

Correct answer:

\(\displaystyle \frac{56}{3}\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(7^2x-\frac{x^3}{3})|_{-6}^{-5}\)

\(\displaystyle V=\pi(7^2(-5)-\frac{(-5)^3}{3})-\pi(7^2(-6)-\frac{(-6)^3}{3})\)

\(\displaystyle V=\frac{56}{3}\pi\)

 

Example Question #32 : Volume

Sphere segment

A sphere with a radius of 7 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 3 units to the left of the origin and the second cut is 2 units to the left of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle \frac{44}{3}\pi\)

\(\displaystyle \frac{128}{3}\pi\)

\(\displaystyle \frac{56}{3}\pi\)

\(\displaystyle \frac{125}{3}\pi\)

\(\displaystyle \frac{59}{3}\pi\)

Correct answer:

\(\displaystyle \frac{128}{3}\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(7^2x-\frac{x^3}{3})|_{-3}^{-2}\)

\(\displaystyle V=\pi(7^2(-2)-\frac{(-2)^3}{3})-\pi(7^2(-3)-\frac{(-3)^3}{3})\)

\(\displaystyle V=\frac{128}{3}\pi\)

 

Example Question #33 : Volume

Sphere segment

A sphere with a radius of 4 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 3 units to the left of the origin and the second cut is 3 units to the right of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle 52\pi\)

\(\displaystyle 74\pi\)

\(\displaystyle 0\)

\(\displaystyle 78\pi\)

\(\displaystyle 37\pi\)

Correct answer:

\(\displaystyle 78\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(4^2x-\frac{x^3}{3})|_{-3}^{3}\)

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

\(\displaystyle V=78\pi\)

 

Example Question #34 : Volume

Sphere segment

A sphere with a radius of 12 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 6 units to the left of the origin and the second cut is 3 units to the left of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle 205\pi\)

\(\displaystyle 369\pi\)

\(\displaystyle 41\pi\)

\(\displaystyle 246\pi\)

\(\displaystyle 123\pi\)

Correct answer:

\(\displaystyle 369\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(12^2x-\frac{x^3}{3})|_{-6}^{-3}\)

\(\displaystyle V=\pi(12^2(-3)-\frac{(-3)^3}{3})-\pi(12^2(-6)-\frac{(-6)^3}{3})\)

\(\displaystyle V=369\pi\)

 

 

Example Question #35 : Volume

Sphere segment

A sphere with a radius of 11 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 3  units to the left of the origin and the second cut is at the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle 127\pi\)

\(\displaystyle 324\pi\)

\(\displaystyle 243\pi\)

\(\displaystyle 81\pi\)

\(\displaystyle 354\pi\)

Correct answer:

\(\displaystyle 354\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(11^2x-\frac{x^3}{3})|_{-3}^{0}\)

\(\displaystyle V=\pi(11^2(0)-\frac{(0)^3}{3})-\pi(11^2(-3)-\frac{(-3)^3}{3})\)

\(\displaystyle V=354\pi\)

 

Example Question #36 : Volume

Sphere segment

A sphere with a radius of 2 has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is 1 unit to the left of the origin and the second cut is 1 unit to the right of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle \frac{22}{3}\pi\)

\(\displaystyle 6\pi\)

\(\displaystyle 8\pi\)

\(\displaystyle \frac{16}{3}\pi\)

\(\displaystyle \frac{20}{3}\pi\)

Correct answer:

\(\displaystyle \frac{22}{3}\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(2^2x-\frac{x^3}{3})|_{-1}^{1}\)

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

\(\displaystyle V=\frac{22}{3}\pi\)

 

Example Question #37 : Volume

Sphere segment

A sphere with a radius of six has a segment with perpendicular planes cut out of it, such as is pictured above.

If the first cut is six units to the left of the origin and the second cut is three units to the left of the origin, what is the volume of the segment?

Possible Answers:

\(\displaystyle 45\pi\)

\(\displaystyle 72\pi\)

\(\displaystyle 28\pi\)

\(\displaystyle 144\pi\)

\(\displaystyle 54\pi\)

Correct answer:

\(\displaystyle 45\pi\)

Explanation:

To approach this problem, begin by picturing how the sphere might be projected onto the two-dimensional Cartesian plane:

Sphere segment outlined

In its two-dimensional projection, we notice the outline of a circle. The formula for a circle of radius \(\displaystyle r\) in the Cartesian coordinate system is given as:

\(\displaystyle x^2+y^2=r^2\)

Which can be rewritten in terms of \(\displaystyle y\) as \(\displaystyle y=\sqrt{r^2-x^2}\)

Now note the disk method of volume creation wherein we rotate a function around an axis (for instance, the x-axis):

\(\displaystyle V=\int_{a}^{b}\pi f^2(x)dx\)

The new function in the integral is akin to the formula of the volume of a cylinder:

\(\displaystyle \pi hr_{cylinder}^2\) where \(\displaystyle r_{cylinder}^2\rightarrow f^2(x)\) and \(\displaystyle h \rightarrow dx\)

The integral sums up these thin cylinders to give the volume of the shape.

Treating \(\displaystyle y\) as our \(\displaystyle f(x)\), this integral can be written as:

\(\displaystyle V=\int_{a}^{b}\pi(r^2-x^2)dx\)

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{a}^{b}\)

Consider the points where circle contacts the x-axis, the greatest and smallest possible values of \(\displaystyle x\) on the circle:

\(\displaystyle V=\pi(r^2x-\frac{x^3}{3})|_{-r}^{r}\)

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

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

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

This is how the volume of a sphere can be derived, and similary, this is how we can derive the area of our segment:

\(\displaystyle V=\pi(6^2x-\frac{x^3}{3})|_{-6}^{-3}\)

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

\(\displaystyle V=45\pi\)

 

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