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Section 6.5 : More Volume Problems

  1. Find the volume of a pyramid of height \(h\) whose base is an equilateral triangle of length \(L\). Solution
  2. Find the volume of the solid whose base is a disk of radius \(r\) and whose cross-sections are squares. See figure below to see a sketch of the cross-sections.
    A sketch showing a typical cross-section of the solid.  The base of the solid is the disk \({x^2} + {y^2} = {r^2}\), drawn in perspective as an ellipse, and a shaded square stands vertically on the disk with its base running across the disk.  The distance from the center of the disk out along the base is labeled \(x\) and half the width of the square is labeled \(y\).
    Solution
  3. Find the volume of the solid whose base is the region bounded by \(x = 2 - {y^2}\) and \(x = {y^2} - 2\) and whose cross-sections are isosceles triangles with the base perpendicular to the \(y\)-axis and the angle between the base and the two sides of equal length is \(\frac{\pi }{4}\). See figure below to see a sketch of the cross-sections.
    A sketch showing a typical cross-section of the solid.  The base of the solid is the region between the two parabolas \(x = {y^2} - 2\) and \(x = 2 - {y^2}\), drawn in perspective, and a shaded isosceles triangle stands vertically on the base with its base running across the region.  The two base angles of the triangle are each labeled \(\frac{\pi }{4}\), the distance out along the base is labeled \(x\) and half the width is labeled \(y\).
    Solution
  4. Find the volume of a wedge cut out of a “cylinder” whose base is the region bounded by \(y = \sqrt {4 - x} \), \(x = - 4\) and the \(x\)-axis. The angle between the top and bottom of the wedge is \(\frac{\pi }{3}\). See the figure below for a sketch of the “cylinder” and the wedge (the positive \(x\)-axis and positive \(y\)-axis are shown in the sketch – they are just in a different orientation).
    Two sketches side by side.  The one on the left, labeled Cylinder, shows the solid whose base is the region bounded by \(y = \sqrt {4 - x} \), \(x = - 4\) and the x-axis, drawn as a tall vertical column standing on that base.  The one on the right, labeled Wedge, shows the thin wedge cut out of that column by a plane through the x-axis making an angle of \(\frac{\pi }{3}\) with the base.  In both sketches the curve \(y = \sqrt {4 - x} \) and the line \(x = - 4\) are labeled and the angle \(\frac{\pi }{3}\) is marked at the near corner.
    Solution