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Volumes with cross-sections

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54949112
A solid extends from \(x=0\) to \(x=3\), where \(x\) is measured in inches. Its cross-sectional area perpendicular to the x-axis is \(A(x)=5+2x-x^2\) square inches. Find the volume.

Hints

- The area function is already provided, so no base-width conversion is needed. - Integrating square units over inches gives cubic inches.

Solution

1. Volume accumulates cross-sectional area: \(V=\int_0^3A(x)\,\mathrm{d}x\). 2. \(V=\int_0^3(5+2x-x^2)\,\mathrm{d}x=15\,\text{in}^3\).

Answer

\(15\,\text{in}^3\)
54950312
A solid extends from \(x=0\) to \(x=2\). Each perpendicular cross section is a circle. The radius of a representative cross section is labeled in the diagram. Find the volume.
Figure for problem 549503

Hints

- Read the radius expression from the representative cross section. - Use that radius in the circle-area formula. - Accumulate the circular areas from \(x=0\) to \(x=2\).

Solution

1. The diagram gives the radius \(r(x)=2-x\). 2. The cross-sectional area is \(A(x)=\pi(2-x)^2\). 3. Therefore, \(V=\pi\int_0^2(2-x)^2\,\mathrm{d}x=\frac{8\pi}{3}\).

Answer

\(\frac{8\pi}{3}\) cubic units
55607212
The graph shows a base region and a representative vertical segment at \(x=0.5\). Cross sections perpendicular to the x-axis are squares. Find the side length and area of the square cross section at \(x=0.5\).
Figure for problem 556072

Hints

- Read the vertical distance across the base at the marked x-value. - That distance is a side length, not yet an area. - How do you convert a square's side length into its area?

Solution

1. At \(x=0.5\), the displayed vertical segment runs from \(y=0\) to \(y=1.5\), so its length is \(\frac{3}{2}\) units. 2. That segment is the side of the square cross section, so the area is \(\left(\frac{3}{2}\right)^2=\frac{9}{4}\) square units.

Answer

Side length: \(\frac{3}{2}\) units Cross-sectional area: \(\frac{9}{4}\) square units
55607312
A semicircular cross section is one half of the displayed circle, and the labeled segment is its diameter. Find the area of the semicircular cross section.
Figure for problem 556073

Hints

- The labeled segment gives the full diameter, not the radius. - How are diameter and radius related? - A semicircle uses half of the corresponding circle's area.

Solution

1. The displayed diameter is \(6\,\text{cm}\), so the radius is \(3\,\text{cm}\). 2. A semicircle has half the area of a circle, so \(A=\frac{1}{2}\pi(3)^2=\frac{9\pi}{2}\,\text{cm}^2\).

Answer

\(\frac{9\pi}{2}\,\text{cm}^2\)
54949012
The shaded base is the triangular region bounded by \(y=0\), \(y=2-x\), and \(x=0\). Cross sections perpendicular to the x-axis are regular hexagons whose short diagonals equal the vertical base width. Use \(A=\frac{\sqrt3}{2}d^2\) for a regular hexagon with short diagonal \(d\). Find the volume.
Figure for problem 549490

Hints

- Use the vertical width of the triangular base as the short diagonal. - Substitute that variable diagonal into the supplied hexagon-area formula. - Integrate from \(x=0\) to the x-intercept of \(y=2-x\).

Solution

1. The short diagonal is the vertical base width \(d(x)=2-x\). 2. The cross-sectional area is \(A(x)=\frac{\sqrt3}{2}(2-x)^2\). 3. Therefore, \(V=\frac{\sqrt3}{2}\int_0^2(2-x)^2\,\mathrm{d}x=\frac{4\sqrt3}{3}\).

Answer

\(\frac{4\sqrt3}{3}\) cubic units
54949512
Two solids have the same base region and the same slicing interval. Solid S has square cross sections whose sides equal the base width. Solid C has circular cross sections whose diameters equal that same width. Compare their volumes without knowing the base curves.

Hints

- Compare the two cross-sectional areas for the same width. - The ratio between the areas is constant at every slice. - A constant cross-sectional area ratio gives the same volume ratio.

Solution

1. At each slice, \(A_S=w^2\). 2. At the same slice, \(A_C=\frac{\pi}{4}w^2\). 3. Therefore, \(A_C=\frac{\pi}{4}A_S\) at every position. 4. Integrating gives \(V_C=\frac{\pi}{4}V_S\). Since \(\frac{\pi}{4}<1\), Solid S has the larger volume.

Answer

\(V_C=\frac{\pi}{4}V_S\); Solid S has the larger volume.
54949612
A base has vertical width \(w(x)=2\sin x\) on \([0,\pi]\), and perpendicular cross sections are squares. Andrei writes \(V=\int_0^\pi4w(x)\,\mathrm{d}x\). Identify the error and find the correct volume.

Hints

- What two-dimensional quantity must be accumulated to obtain volume? - How is the area of a square related to its side length \(w(x)\)? - After correcting the area function, integrate it over the given slicing interval.

Solution

1. The expression \(4w(x)\) is the square's perimeter, not its area. 2. The correct cross-sectional area is \(A(x)=w(x)^2=4\sin^2x\). 3. Therefore, \(V=\int_0^\pi4\sin^2x\,\mathrm{d}x=2\pi\).

Answer

Andrei integrated perimeter. The correct volume is \(2\pi\) cubic units.
54949912
For \(0\le x\le9\), each cross section of a solid is a triangle with base \(\sqrt{x}\) and constant altitude \(5\). Find the volume.

Hints

- Use the two distinct triangle dimensions exactly as given. - Only the base varies with position.

Solution

1. The cross-sectional area is \(A(x)=\frac12(\sqrt x)(5)=\frac52\sqrt x\). 2. \(V=\int_0^9\frac52\sqrt x\,\mathrm{d}x=45\).

Answer

\(45\) cubic units
54950012
A base has vertical width \(w(x)=\cos x\) for \(-\frac{\pi}{2}\le x\le\frac{\pi}{2}\). Perpendicular cross sections are rectangles whose height is twice the base width. Find the volume.

Hints

- Use \(w(x)\) and \(2w(x)\) as the two rectangle dimensions. - Multiply the dimensions before integrating. - Use symmetry or a power-reduction identity to evaluate the cosine-squared integral.

Solution

1. Each cross-sectional area is \(A(x)=w(x)\cdot2w(x)=2\cos^2x\). 2. Therefore, \(V=\int_{-\pi/2}^{\pi/2}2\cos^2x\,\mathrm{d}x=\pi\).

Answer

\(\pi\) cubic units
54951512
A base has vertical width \(w(x)=e^{-x^2}\) on \([0,2]\). Cross sections perpendicular to the x-axis are squares. Use a calculator to find the volume to three decimal places.

Hints

- Square the entire width function. - Set up the exact integral before using numerical technology.

Solution

1. The cross-sectional area is \(A(x)=e^{-2x^2}\). 2. \(V=\int_0^2e^{-2x^2}\,\mathrm{d}x\). 3. Numerical evaluation gives \(V\approx0.627\) cubic units.

Answer

\(\approx0.627\) cubic units
54951912
Two solids share the same base and use the same base width \(w(x)\) as a side length. One has square cross sections; the other has equilateral-triangle cross sections. If the square-cross-section volume is \(40\), find the other volume.

Hints

- Compare shape area formulas using the same side length. - Carry the constant ratio from slices to the entire solid.

Solution

1. Square area is \(w(x)^2\). 2. Equilateral-triangle area is \(\frac{\sqrt3}{4}w(x)^2\). 3. The same constant ratio holds after integration. 4. The triangle-cross-section volume is \(\frac{\sqrt3}{4}(40)=10\sqrt3\).

Answer

\(10\sqrt3\) cubic units
54952112
A solid has isosceles-triangle cross sections perpendicular to the x-axis. At each \(x\in[0,3]\), both the triangle's base and altitude equal \(3-x\). Find the volume.

Hints

- Use the two equal but perpendicular triangle dimensions. - The one-half factor remains part of every cross-sectional area.

Solution

1. The area is \(A(x)=\frac12(3-x)(3-x)=\frac12(3-x)^2\). 2. \(V=\frac12\int_0^3(3-x)^2\,\mathrm{d}x=\frac{9}{2}\).

Answer

\(\frac{9}{2}\) cubic units
54952512
For a certain base region, \(\int_a^b w(x)^2\,\mathrm{d}x=12\), where \(w(x)\) is the base width. A designer needs volume \(\frac{3\pi}{2}\). Which cross-section choice produces that volume? A. Squares with side \(w\) B. Circles with diameter \(w\) C. Semicircles with diameter \(w\) D. Equilateral triangles with side \(w\)

Hints

- Factor each shape's area into a constant times the squared width. - Use the supplied integral once for each possible constant.

Solution

1. The shape factors multiplying \(w^2\) are \(1\), \(\frac{\pi}{4}\), \(\frac{\pi}{8}\), and \(\frac{\sqrt3}{4}\), respectively. 2. Multiplying by \(\int_a^b w(x)^2\,\mathrm{d}x=12\), option C gives \(12\cdot\frac{\pi}{8}=\frac{3\pi}{2}\). 3. Therefore, semicircles with diameter \(w\) meet the design requirement.

Answer

Choice C: semicircles with diameter \(w\).
55607412
The graph shows the base of a solid. Cross sections perpendicular to the x-axis are equilateral triangles whose side length is the vertical width of the base. Write the cross-sectional area function \(A(x)\) and the volume integral. Do not evaluate the integral.
Figure for problem 556074

Hints

- Read the vertical distance between the two displayed curves. - That distance is the side length, not the area, of each equilateral triangle. - Apply the equilateral-triangle area formula before integrating.

Solution

1. On \(0\le x\le2\), the vertical width is \(s(x)=2x-x^2\). 2. An equilateral triangle with side \(s\) has area \(\frac{\sqrt3}{4}s^2\), so \(A(x)=\frac{\sqrt3}{4}(2x-x^2)^2\). 3. The volume setup is \(V=\int_0^2\frac{\sqrt3}{4}(2x-x^2)^2\,\mathrm{d}x\).

Answer

\(A(x)=\frac{\sqrt3}{4}(2x-x^2)^2\) \(V=\int_0^2\frac{\sqrt3}{4}(2x-x^2)^2\,\mathrm{d}x\)
54948212
The shaded base of a solid lies between \(y=\sqrt{x}\) and \(y=\frac{x}{2}\) for \(0\le x\le4\). Cross sections perpendicular to the x-axis are squares. Find the volume.
Figure for problem 549482

Hints

- Use the vertical distance between the two base curves as the square's side length. - Square that distance to obtain cross-sectional area. - Integrate the cross-sectional area over \(0\le x\le4\).

Solution

1. The side length of a square is the vertical width of the base: \(s(x)=\sqrt x-\frac{x}{2}\). 2. The cross-sectional area is \(A(x)=s(x)^2\). 3. Therefore, \(V=\int_0^4\left(\sqrt x-\frac{x}{2}\right)^2\,\mathrm{d}x=\frac{8}{15}\).

Answer

\(\frac{8}{15}\) cubic units
54948312
The shaded base of a solid lies between \(y=3\) and \(y=x^2\). Each cross section perpendicular to the x-axis is a rectangle whose height is three times its base in the xy-plane. Find the volume.
Figure for problem 549483

Hints

- Find the x-interval from the intersections of the base curves. - Use \(3-x^2\) as the rectangle's base dimension. - Multiply the two rectangle dimensions before integrating.

Solution

1. The base width is \(b(x)=3-x^2\), and the curves intersect at \(x=\pm\sqrt3\). 2. The rectangle height is \(3b(x)\), so its area is \(A(x)=b(x)\cdot3b(x)=3(3-x^2)^2\). 3. Therefore, \(V=\int_{-\sqrt3}^{\sqrt3}3(3-x^2)^2\,\mathrm{d}x=\frac{144\sqrt3}{5}\).

Answer

\(\frac{144\sqrt3}{5}\) cubic units
54948412
The shaded base of a solid is enclosed by \(y=x\) and \(y=x^2\) in the first quadrant. Cross sections perpendicular to the x-axis are equilateral triangles whose sides lie in the base. Find the exact volume.
Figure for problem 549484

Hints

- Use the vertical separation of the base curves as the triangle's side length. - Apply the equilateral-triangle area formula to that variable side. - Integrate from the two intersection x-values.

Solution

1. The curves intersect at \(x=0\) and \(x=1\), and the triangle side length is \(s(x)=x-x^2\). 2. The cross-sectional area is \(A(x)=\frac{\sqrt3}{4}s(x)^2\). 3. Therefore, \(V=\frac{\sqrt3}{4}\int_0^1(x-x^2)^2\,\mathrm{d}x=\frac{\sqrt3}{120}\).

Answer

\(\frac{\sqrt3}{120}\) cubic units
54948512
The shaded base of a solid is bounded by \(y=4\) and \(y=x^2\). Cross sections perpendicular to the x-axis are semicircles whose diameters lie in the base. Find the volume.
Figure for problem 549485

Hints

- Use the vertical base width as the semicircle's diameter, not its radius. - Express semicircle area in terms of the diameter. - Integrate over the full interval from \(x=-2\) to \(x=2\).

Solution

1. The diameter is \(d(x)=4-x^2\) for \(-2\le x\le2\). 2. A semicircle with diameter \(d\) has area \(A=\frac{\pi}{8}d^2\). 3. Therefore, \(V=\frac{\pi}{8}\int_{-2}^{2}(4-x^2)^2\,\mathrm{d}x=\frac{64\pi}{15}\).

Answer

\(\frac{64\pi}{15}\) cubic units
54948612
For \(-1\le x\le1\), a base region has vertical width \(w(x)=1-x^2\). Cross sections perpendicular to the x-axis are regular hexagons whose long diagonals equal \(w(x)\). The long diagonal of a regular hexagon is twice its side length. a) Write the cross-sectional area \(A(x)\). b) Find the exact volume.
Figure for problem 549486

Hints

- Convert the long diagonal into the side length of the regular hexagon. - The cross-sectional area depends on the square of the base width. - Use symmetry when evaluating the volume integral.

Solution

1. If the long diagonal is \(w(x)\), then the hexagon side length is \(s(x)=\frac{w(x)}{2}\). 2. Using \(A=\frac{3\sqrt3}{2}s^2\), the cross-sectional area is \(A(x)=\frac{3\sqrt3}{8}(1-x^2)^2\). 3. The volume is \(V=\frac{3\sqrt3}{8}\int_{-1}^{1}(1-x^2)^2\,\mathrm{d}x\). 4. Since \(\int_{-1}^{1}(1-x^2)^2\,\mathrm{d}x=\frac{16}{15}\), \(V=\frac{2\sqrt3}{5}\).

Answer

a) \(A(x)=\frac{3\sqrt3}{8}(1-x^2)^2\) b) \(\frac{2\sqrt3}{5}\) cubic units
54948712
The shaded base is enclosed by \(x=2y\) and \(x=y^2\). Cross sections perpendicular to the y-axis are squares. Find the volume.
Figure for problem 549487

Hints

- Cross sections perpendicular to the y-axis use horizontal base widths. - Subtract \(x=y^2\) from \(x=2y\) to obtain the square's side. - Square the side length before integrating with respect to \(y\).

Solution

1. The curves intersect at \(y=0\) and \(y=2\). 2. The square side is the horizontal width \(s(y)=2y-y^2\). 3. Therefore, \(V=\int_0^2(2y-y^2)^2\,\mathrm{d}y=\frac{16}{15}\).

Answer

\(\frac{16}{15}\) cubic units
54948812
The shaded base lies between \(x=y^2\) and \(x=4\) for \(-2\le y\le2\). Cross sections perpendicular to the y-axis are rectangles. Each rectangle has base equal to the horizontal width of the region and height \(y+3\). Find the volume.
Figure for problem 549488

Hints

- Use the horizontal distance from \(x=y^2\) to \(x=4\) as one rectangle dimension. - Use the separately stated height \(y+3\) as the other dimension. - Integrate the product over \(-2\le y\le2\).

Solution

1. The rectangle base is \(b(y)=4-y^2\), and its other dimension is \(y+3\). 2. Thus, the cross-sectional area is \(A(y)=(4-y^2)(y+3)\). 3. Therefore, \(V=\int_{-2}^{2}(4-y^2)(y+3)\,\mathrm{d}y=32\).

Answer

\(32\) cubic units
54948912
For \(0\le x\le3\), the shaded base lies between \(y=x\) and \(y=3-x\). Cross sections perpendicular to the x-axis are squares. Find the volume, explaining why the boundary switch does not require splitting the final integral.
Figure for problem 549489

Hints

- A side length is a distance, so use an absolute value when the upper line changes. - Squaring an absolute value gives the same result as squaring its expression. - Locate the line intersection to explain the change in geometric order.

Solution

1. The vertical distance between the lines is \(s(x)=|(3-x)-x|=|3-2x|\). 2. A square cross section has area \(A(x)=s(x)^2=|3-2x|^2=(3-2x)^2\). 3. Squaring removes the sign, so one area formula works across the intersection at \(x=\frac{3}{2}\). 4. Therefore, \(V=\int_0^3(3-2x)^2\,\mathrm{d}x=9\).

Answer

\(9\) cubic units
54949212
The shaded base region is shown. Cross sections perpendicular to the x-axis are squares. Find the volume.
Figure for problem 549492

Hints

- Use two grid points on each line to determine its equation. - Subtract the lower y-value from the upper y-value to get the square side. - Square the side length and integrate to the intersection.

Solution

1. From the graph, the upper boundary is \(y=3-\frac{1}{2}x\) and the lower boundary is \(y=\frac{1}{2}x\). Thus, the square side length is \(s(x)=3-x\). 2. The boundaries meet at \(x=3\). 3. Therefore, \(V=\int_0^3(3-x)^2\,\mathrm{d}x=9\).

Answer

\(9\) cubic units
54949312
For \(0\le x\le1\), the vertical width of a base region is \(w(x)=kx(1-x)\), where \(k>0\). Cross sections perpendicular to the x-axis are squares. If the volume is \(\frac{6}{5}\), find \(k\).

Hints

- The square side length is the given vertical width. - Squaring the width makes the volume depend on \(k^2\). - Use \(k>0\) after solving the volume equation.

Solution

1. The square area is \(A(x)=k^2x^2(1-x)^2\). 2. Therefore, \(V=k^2\int_0^1x^2(1-x)^2\,\mathrm{d}x=\frac{k^2}{30}\). 3. Set \(\frac{k^2}{30}=\frac{6}{5}\). Then \(k^2=36\), and \(k=6\) because \(k>0\).

Answer

\(k=6\)
54949412
A solid has cross sections perpendicular to the x-axis that are semicircles with diameter \(d(x)=x\), from \(x=0\) to \(x=b\). The volume is \(9\pi\). Find \(b\).

Hints

- Express the volume in terms of the unknown endpoint. - Cancel the common geometric constant before solving.

Solution

1. The cross-sectional area is \(A(x)=\frac{\pi}{8}x^2\). 2. \(V=\frac{\pi}{8}\int_0^b x^2\,\mathrm{d}x=\frac{\pi b^3}{24}\). 3. Set \(\frac{\pi b^3}{24}=9\pi\), giving \(b^3=216\) and \(b=6\).

Answer

\(b=6\)
54949712
A model solid has base region between \(y=2-\frac{x}{2}\) and \(y=0\) for \(0\le x\le4\). Cross sections perpendicular to the x-axis are squares. One coordinate unit represents \(2\,\text{cm}\) in the actual object. Find the actual volume.

Hints

- What is the vertical distance between the two base boundaries at position \(x\)? - Compute the model volume before applying the physical scale factor. - How does volume scale when every linear dimension is multiplied by \(2\)?

Solution

1. In coordinate units, \(V_m=\int_0^4\left(2-\frac{x}{2}\right)^2\,\mathrm{d}x=\frac{16}{3}\). 2. A linear scale factor of \(2\) multiplies volume by \(2^3=8\). 3. Therefore, the actual volume is \(8V_m=\frac{128}{3}\,\text{cm}^3\).

Answer

\(\frac{128}{3}\,\text{cm}^3\)
54950112
A base lies between \(y=1\) and \(y=x^2\). Cross sections perpendicular to the x-axis are right triangles. One leg equals the base width, and the other leg is twice that width. Find the volume.

Hints

- How do the two base curves determine the vertical width at a given \(x\)? - Express both triangle legs in terms of that width before finding area. - Volume is the integral of the resulting cross-sectional area.

Solution

1. The base width is \(w(x)=1-x^2\) for \(-1\le x\le1\). 2. The triangle area is \(A(x)=\frac{1}{2}w(x)[2w(x)]=w(x)^2\). 3. Therefore, \(V=\int_{-1}^{1}(1-x^2)^2\,\mathrm{d}x=\frac{16}{15}\).

Answer

\(\frac{16}{15}\) cubic units
54950212
A base lies between \(y=\sin x\) and the x-axis on \([0,\pi]\). Cross sections perpendicular to the x-axis are semicircles whose diameters lie in the base. Find the exact volume.

Hints

- The vertical base width is the semicircle's diameter, not its radius. - Write semicircle area in terms of diameter before integrating. - What is \(\int_0^\pi\sin^2x\,\mathrm{d}x\)?

Solution

1. The diameter is \(d(x)=\sin x\). 2. The cross-sectional area is \(A(x)=\frac{\pi}{8}\sin^2x\). 3. Therefore, \(V=\frac{\pi}{8}\int_0^\pi\sin^2x\,\mathrm{d}x=\frac{\pi^2}{16}\).

Answer

\(\frac{\pi^2}{16}\) cubic units
54950412
The base is bounded by \(y=4\) and \(y=x^2\). Perpendicular cross sections are squares whose diagonals, rather than sides, lie in the base. The diagram shows one cross section. Find the volume.
Figure for problem 549504

Hints

- Use the base width as the square's diagonal, not its side. - Express square area in terms of diagonal length. - Integrate over the intersections \(x=-2\) and \(x=2\).

Solution

1. The square diagonal is the vertical base width \(d(x)=4-x^2\). 2. A square with diagonal \(d\) has area \(A=\frac{d^2}{2}\). 3. Therefore, \(V=\frac{1}{2}\int_{-2}^{2}(4-x^2)^2\,\mathrm{d}x=\frac{256}{15}\).

Answer

\(\frac{256}{15}\) cubic units
54950512
A base is bounded by \(x=0\), \(x=4-y\), \(y=0\), and \(y=4\). Cross sections perpendicular to the y-axis are circles whose circumferences equal the horizontal widths of the base. Find the volume.

Hints

- What is the horizontal width of the base at height \(y\)? - Convert circumference to radius before calculating circle area. - Integrate with respect to \(y\) over the full height of the base.

Solution

1. At height \(y\), the horizontal width is \(w(y)=4-y\). 2. If a circle's circumference is \(w(y)\), then its radius is \(r(y)=\frac{4-y}{2\pi}\). 3. The cross-sectional area is \(A(y)=\pi[r(y)]^2=\frac{(4-y)^2}{4\pi}\). 4. Therefore, \(V=\frac{1}{4\pi}\int_0^4(4-y)^2\,\mathrm{d}y=\frac{16}{3\pi}\).

Answer

\(\frac{16}{3\pi}\) cubic units
54950612
A base has vertical width \(x\) for \(0\le x\le3\). Each cross section perpendicular to the x-axis is a rectangle with one side equal to that width. The representative cross section shows its diagonal length. Find the volume.
Figure for problem 549506

Hints

- Read the fixed diagonal length from the representative cross section. - How can the diagonal and the two rectangle side lengths be related? - Build the rectangular area function before integrating.

Solution

1. One side of a cross-sectional rectangle is \(x\). The diagram gives diagonal length \(5\). If the other side is \(h(x)\), then \(x^2+[h(x)]^2=25\), so \(h(x)=\sqrt{25-x^2}\). 2. The cross-sectional area is \(A(x)=x\sqrt{25-x^2}\). 3. The volume is \(V=\int_0^3x\sqrt{25-x^2}\,\mathrm{d}x\). 4. Evaluating gives \(V=\frac{1}{3}(125-64)=\frac{61}{3}\).

Answer

\(\frac{61}{3}\) cubic units
54950712
In the first quadrant, the shaded base lies between \(y=x\) and \(y=x^2\). Cross sections perpendicular to the y-axis are semicircles whose diameters lie in the base. Find the volume.
Figure for problem 549507

Hints

- Rewrite both base curves as x-functions of y. - Use the horizontal base width as the semicircle diameter. - Express semicircle area in terms of diameter before integrating.

Solution

1. Rewrite the boundaries as \(x=y\) and \(x=\sqrt y\). 2. The horizontal diameter is \(d(y)=\sqrt y-y\) for \(0\le y\le1\). 3. Therefore, \(V=\frac{\pi}{8}\int_0^1(\sqrt y-y)^2\,\mathrm{d}y=\frac{\pi}{240}\).

Answer

\(\frac{\pi}{240}\) cubic units
54950912
The shaded base of a solid is the disk \(x^2+y^2\le9\). Cross sections perpendicular to the x-axis are squares. Find the volume.
Figure for problem 549509

Hints

- Solve the circle equation for the upper and lower y-values. - Use the full vertical chord, not one radius, as the square side. - Square the chord length before integrating across the disk.

Solution

1. At position \(x\), the disk's vertical chord has length \(s(x)=2\sqrt{9-x^2}\). 2. The square area is \(A(x)=4(9-x^2)\). 3. Therefore, \(V=\int_{-3}^{3}4(9-x^2)\,\mathrm{d}x=144\).

Answer

\(144\) cubic units
54951012
The shaded base of a solid is the disk \(x^2+y^2\le4\). Cross sections perpendicular to the x-axis are semicircles whose diameters are vertical chords of the disk. Find the volume.
Figure for problem 549510

Hints

- Solve the circle equation for both vertical endpoints of a chord. - Use the full chord as the semicircle diameter. - Simplify the squared radical before integrating.

Solution

1. The chord length is \(d(x)=2\sqrt{4-x^2}\). 2. The semicircle area is \(A(x)=\frac{\pi}{8}d(x)^2=\frac{\pi}{2}(4-x^2)\). 3. Therefore, \(V=\frac{\pi}{2}\int_{-2}^{2}(4-x^2)\,\mathrm{d}x=\frac{16\pi}{3}\).

Answer

\(\frac{16\pi}{3}\) cubic units
54951112
A triangular base has vertices \((0,0)\), \((3,0)\), and \((0,3)\). Cross sections perpendicular to the x-axis are squares. a) Write the cross-sectional area function \(A(x)\). b) Use \(V=\int A(x)\,\mathrm{d}x\) to find the exact volume. c) Identify the standard solid formed and verify the same volume with its geometric volume formula.

Hints

- Determine the vertical width of the triangular base at a general x-value. - That width is a square side length, so how is \(A(x)\) related to it? - After integrating, compare the dimensions with a familiar pyramid formula.

Solution

1. The slanted boundary through \((0,3)\) and \((3,0)\) is \(y=3-x\), so each square has side length \(s(x)=3-x\) for \(0\le x\le3\). 2. Therefore, \(A(x)=(3-x)^2\). 3. Using cross-sectional integration, \(V=\int_0^3(3-x)^2\,\mathrm{d}x=9\). 4. The linearly shrinking square sections form a square pyramid with base side \(3\) and height \(3\). Its geometric formula gives \(\frac{1}{3}(3^2)(3)=9\), confirming the integral.

Answer

a) \(A(x)=(3-x)^2\) b) \(V=\int_0^3(3-x)^2\,\mathrm{d}x=9\) cubic units c) The solid is a square pyramid, and \(\frac{1}{3}(3^2)(3)=9\) cubic units.
54951212
A sculptural beam extends from \(x=0\) to \(x=\pi\), where \(x\) is measured in feet. Its base has vertical width \(w(x)=2+\sin x\) feet. Cross sections perpendicular to the x-axis are equilateral triangles with side \(w(x)\). a) Write the cross-sectional area \(A(x)\). b) Find the exact volume of the beam.

Hints

- What is the area formula for an equilateral triangle in terms of its side length? - Substitute the given width function before forming the volume integral. - How can \(\sin^2x\) be integrated over \([0,\pi]\)?

Solution

1. The area of an equilateral triangle with side \(w\) is \(\frac{\sqrt3}{4}w^2\), so \(A(x)=\frac{\sqrt3}{4}(2+\sin x)^2\). 2. The volume is \(V=\frac{\sqrt3}{4}\int_0^\pi(2+\sin x)^2\,\mathrm{d}x\). 3. Expand and integrate: \(\int_0^\pi(4+4\sin x+\sin^2x)\,\mathrm{d}x=4\pi+8+\frac{\pi}{2}=8+\frac{9\pi}{2}\). 4. Therefore, \(V=2\sqrt3+\frac{9\pi\sqrt3}{8}\,\text{ft}^3\).

Answer

a) \(A(x)=\frac{\sqrt3}{4}(2+\sin x)^2\) b) \(2\sqrt3+\frac{9\pi\sqrt3}{8}\,\text{ft}^3\)
54951312
Square cross sections of a solid have side lengths measured at several x-values. <table><tr><td>\(x\)</td><td>\(0\)</td><td>\(1\)</td><td>\(3\)</td><td>\(5\)</td></tr><tr><td>side \(s(x)\)</td><td>\(0\)</td><td>\(2\)</td><td>\(3\)</td><td>\(1\)</td></tr></table> Convert the side lengths to cross-sectional areas, then use the trapezoidal rule on those area values to estimate the volume.

Hints

- What area corresponds to each measured square side length? - Use the actual interval widths \(1\), \(2\), and \(2\). - Apply the trapezoidal rule to cross-sectional area, not directly to side length.

Solution

1. Square the side data to obtain cross-sectional areas \(0\), \(4\), \(9\), and \(1\). 2. Apply trapezoids to \(A(x)\), not to \(s(x)\): \(\frac{1}{2}(0+4)+\frac{2}{2}(4+9)+\frac{2}{2}(9+1)=2+13+10\). 3. Therefore, \(V\approx25\) cubic units.

Answer

\(V\approx25\) cubic units
54951412
Square cross sections are measured at three x-values. <table><tr><td>\(x\)</td><td>\(0\)</td><td>\(2\)</td><td>\(4\)</td></tr><tr><td>side length</td><td>\(1\)</td><td>\(m\)</td><td>\(3\)</td></tr></table> A trapezoidal estimate using the cross-sectional areas gives a volume of \(20\) cubic units. Find \(m>0\).

Hints

- Convert the side lengths to square areas before using the trapezoidal rule. - Each subinterval has width \(2\). - Use the positivity condition after solving for \(m^2\).

Solution

1. The cross-sectional area values are \(1\), \(m^2\), and \(9\). 2. With subinterval width \(2\), the trapezoidal estimate is \((1+m^2)+(m^2+9)=10+2m^2\). 3. Set \(10+2m^2=20\). Then \(m^2=5\), so \(m=\sqrt5\) because \(m>0\).

Answer

\(m=\sqrt5\)
54951612
A base lies between \(y=\cos x\) and \(y=\sin x\) for \(0\le x\le\frac{\pi}{4}\). Cross sections perpendicular to the x-axis are squares. Find the exact volume.

Hints

- Which trigonometric curve is above the other on the stated interval? - The square side is the vertical distance between the curves. - Simplify the squared difference before integrating.

Solution

1. On the interval, \(\cos x\ge\sin x\), so the square side length is \(s(x)=\cos x-\sin x\). 2. The cross-sectional area is \(A(x)=(\cos x-\sin x)^2=1-\sin(2x)\). 3. Therefore, \(V=\int_0^{\pi/4}[1-\sin(2x)]\,\mathrm{d}x=\frac{\pi}{4}-\frac{1}{2}\).

Answer

\(\frac{\pi}{4}-\frac{1}{2}\) cubic units
54951712
A base lies between \(y=e^x\) and \(y=1+x\) on \([0,1]\). Cross sections perpendicular to the x-axis are squares. Find the volume to four decimal places.

Hints

- Determine which base curve is above on \([0,1]\). - Use their vertical separation as the square side length. - Set up the exact integral before using numerical technology.

Solution

1. Since \(e^x\ge1+x\), the square side length is \(s(x)=e^x-1-x\). 2. The cross-sectional area is \(A(x)=(e^x-1-x)^2\), so \(V=\int_0^1(e^x-1-x)^2\,\mathrm{d}x\). 3. Numerical evaluation gives \(V\approx0.0913\) cubic units.

Answer

\(\approx0.0913\) cubic units
54951812
The graph shows the upper and lower boundaries of a base region. Cross sections perpendicular to the x-axis are squares whose diagonals lie in the base. Write and evaluate the volume integral.
Figure for problem 549518

Hints

- Read the square diagonal as the vertical separation in the base. - Express a square's area in terms of its diagonal. - Use symmetry to remove the absolute value before integrating.

Solution

1. The upper boundary is \(y=2\) and the lower boundary is \(y=|x|\), so the square diagonal is \(d(x)=2-|x|\) on \([-2,2]\). 2. A square with diagonal \(d\) has area \(\frac{1}{2}d^2\). Thus, \(A(x)=\frac{1}{2}(2-|x|)^2\). 3. By symmetry, \(V=2\int_0^2\frac{1}{2}(2-x)^2\,\mathrm{d}x=\frac{8}{3}\) cubic units.

Answer

\(\frac{8}{3}\) cubic units
54952012
For \(0\le x\le4\), each cross section is a rectangle. One side has length \(x\), and the rectangle's perimeter is always \(12\). Find the volume.

Hints

- Use the perimeter condition to recover the missing rectangle dimension. - Verify both dimensions stay nonnegative on the interval.

Solution

1. If the other side is \(h(x)\), then \(2[x+h(x)]=12\), so \(h(x)=6-x\). 2. The area is \(A(x)=x(6-x)\). 3. \(V=\int_0^4x(6-x)\,\mathrm{d}x=\frac{80}{3}\).

Answer

\(\frac{80}{3}\) cubic units
54952212
A base lies between \(y=\ln x\) and the x-axis for \(1\le x\le e\). Cross sections perpendicular to the x-axis are squares. Find the exact volume.

Hints

- What is the vertical distance from the x-axis to the logarithmic curve? - Square that distance to form each square cross-sectional area. - Evaluate the logarithmic antiderivative at \(x=1\) and \(x=e\).

Solution

1. The square side length is the vertical distance from the x-axis to the curve: \(s(x)=\ln x\). 2. The cross-sectional area is \(A(x)=(\ln x)^2\), so \(V=\int_1^e(\ln x)^2\,\mathrm{d}x\). 3. An antiderivative is \(x[(\ln x)^2-2\ln x+2]\). Therefore, \(V=e-2\) cubic units.

Answer

\(e-2\) cubic units
54952312
A pedestrian tunnel is \(10\,\text{m}\) long. Cross sections perpendicular to the x-axis are equilateral triangles. The side length decreases linearly from \(6\,\text{m}\) at \(x=0\) to \(2\,\text{m}\) at \(x=10\). a) Find the side-length function \(s(x)\). b) Find the exact volume of the tunnel.

Hints

- Build a linear function from the two endpoint side lengths. - Convert side length into equilateral-triangle area before integrating. - Check that your side function gives the stated endpoint values.

Solution

1. The side length has slope \(\frac{2-6}{10}=-\frac{2}{5}\), so \(s(x)=6-\frac{2}{5}x\). 2. The cross-sectional area is \(A(x)=\frac{\sqrt3}{4}\left(6-\frac{2}{5}x\right)^2\). 3. The volume is \(V=\frac{\sqrt3}{4}\int_0^{10}\left(6-\frac{2}{5}x\right)^2\,\mathrm{d}x\). 4. The integral equals \(\frac{520}{3}\), so \(V=\frac{130\sqrt3}{3}\,\text{m}^3\).

Answer

a) \(s(x)=6-\frac{2}{5}x\) b) \(\frac{130\sqrt3}{3}\,\text{m}^3\)
54952412
A base has vertical width \(w(x)=1-x\) for \(0\le x\le1\). Cross sections are rectangles whose perpendicular height is \((1+x)w(x)\). Find the volume.

Hints

- The aspect ratio changes with x, so keep its factor inside the integral. - Both rectangle dimensions include the base width.

Solution

1. The cross-sectional area is \(A(x)=w(x)[(1+x)w(x)]=(1+x)(1-x)^2\). 2. \(V=\int_0^1(1+x)(1-x)^2\,\mathrm{d}x=\frac{5}{12}\).

Answer

\(\frac{5}{12}\) cubic units
54949812
For \(0\le x\le2\), the accumulated volume of a solid is \(V(x)=x^3-3x^2+4x\). Cross sections perpendicular to the x-axis are squares. Find the square side-length function and the location and value of its shortest side.

Hints

- Differentiate accumulated volume to obtain cross-sectional area. - Take the positive square root of the square's area to obtain its side length. - Minimize the quadratic area expression before taking its square root.

Solution

1. The cross-sectional area is \(V'(x)=3x^2-6x+4\). 2. Since the sections are squares, \(s(x)=\sqrt{3x^2-6x+4}\). 3. Rewrite the area as \(3(x-1)^2+1\), which is minimized at \(x=1\). 4. The shortest side has length \(s(1)=1\).

Answer

\(s(x)=\sqrt{3x^2-6x+4}\); the shortest side is \(1\) unit at \(x=1\).
54950812
The shaded base is bounded by \(x=y^2\), \(x=4\), \(y=0\), and \(y=2\). Cross sections perpendicular to the y-axis are squares. Find the height \(c\) that divides the solid into two equal-volume parts. Round to three decimal places.
Figure for problem 549508

Hints

- Use the horizontal base width as the square side. - Calculate half of the total volume before forming the cut-height equation. - Solve the accumulation equation numerically within \(0<c<2\).

Solution

1. At height \(y\), the square side is \(4-y^2\), so \(A(y)=(4-y^2)^2\). 2. The total volume is \(\int_0^2(4-y^2)^2\,\mathrm{d}y=\frac{256}{15}\). 3. Equal volumes require \(\int_0^c(4-y^2)^2\,\mathrm{d}y=\frac{128}{15}\). 4. Numerical solution on \((0,2)\) gives \(c\approx0.562\).

Answer

\(c\approx0.562\)
55607512
The graph shows the base of a solid. Cross sections perpendicular to the x-axis are squares whose side lengths are the vertical widths of the base. Determine the two width functions required by the graph, then find the exact volume of the solid.
Figure for problem 556075

Hints

- Identify where the lower boundary changes from the slanted line to the x-axis. - On each interval, write vertical width as upper boundary minus lower boundary. - Square each width before integrating, then add the two volume contributions.

Solution

1. For \(-1\le x\le0\), the upper boundary is \(y=4-x^2\) and the lower boundary is \(y=-3x\), so the square side is \(s_1(x)=4+3x-x^2\). 2. For \(0\le x\le2\), the lower boundary is the x-axis, so the side is \(s_2(x)=4-x^2\). 3. Therefore, \(V=\int_{-1}^{0}(4+3x-x^2)^2\,\mathrm{d}x+\int_{0}^{2}(4-x^2)^2\,\mathrm{d}x\). 4. The two integrals are \(\frac{181}{30}\) and \(\frac{256}{15}\), respectively, so \(V=\frac{231}{10}\) cubic units.

Answer

\(s_1(x)=4+3x-x^2\) for \(-1\le x\le0\) \(s_2(x)=4-x^2\) for \(0\le x\le2\) \(V=\frac{231}{10}\) cubic units
55607612
The solid shown is a square pyramid. Let \(z\) measure distance from the apex toward the base along the height. Cross sections perpendicular to the height are squares. Using the dimensions shown, derive the cross-sectional area \(A(z)\), integrate it to find the pyramid's volume, and verify that the result agrees with \(V=\frac{1}{3}Bh\).
Figure for problem 556076

Hints

- Compare a cross-sectional square with the base square using similarity from the apex. - How does side length scale with distance along the pyramid's height? - Integrate cross-sectional area from the apex to the base, then compare with the standard pyramid formula.

Solution

1. The full height is \(9\,\text{cm}\) and the base side length is \(6\,\text{cm}\). By similarity, a square at distance \(z\) from the apex has side length \(s(z)=\frac{6}{9}z=\frac{2}{3}z\). 2. Thus, \(A(z)=s(z)^2=\frac{4}{9}z^2\). 3. The cross-sectional integral gives \(V=\int_0^9\frac{4}{9}z^2\,\mathrm{d}z=108\,\text{cm}^3\). 4. The base area is \(B=6^2=36\,\text{cm}^2\), and \(\frac{1}{3}Bh=\frac{1}{3}(36)(9)=108\,\text{cm}^3\), so the formulas agree.

Answer

\(A(z)=\frac{4}{9}z^2\), and \(V=108\,\text{cm}^3\).

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