Exercises: Identify Cross-Sections and Solids of Revolution
Warm-Up
A cross-section is best described as:
The three-dimensional solid formed when a 2D shape is rotated about an axis
The two-dimensional shape visible when a plane cuts through a three-dimensional object
The outer curved surface of a cylinder or cone
A shape that can only be produced by cutting through the center of an object
A horizontal slice (parallel to the base) is taken through a cone. What shape is the cross-section?
Triangle
Rectangle
Circle
Ellipse
A solid of revolution is created by:
Stacking identical 2D cross-sections on top of each other
Rotating a two-dimensional shape about a line (axis)
Stretching a 2D shape in all three directions equally
Reflecting a 2D shape across a line to form a mirror image
Fluency Practice
A vertical plane passes through the axis of a cylinder (a plane containing the cylinder's central axis). What shape is the cross-section?
Circle
Ellipse
Rectangle
Triangle
A sphere of radius is sliced by a plane at a distance from the center, where . What shape is the cross-section, and how does its size compare to a cross-section through the center?
Circle; larger than the great circle (center cross-section)
Ellipse; smaller than the great circle, because the off-center cut is tilted
Circle; smaller than the great circle (center cross-section)
Circle; the same size as the great circle, because all cross-sections of a sphere are equal
A cylinder is sliced by a plane that is tilted at an angle to the axis (oblique to the axis, not perpendicular and not parallel). What shape is the cross-section?
Circle
Ellipse
Parabola
Rectangle
A right triangle is rotated about its vertical leg. Which solid is produced?
Cylinder
Sphere
Cone
Pyramid
A rectangle with width 3 cm and height 8 cm is rotated about its longer edge (height = 8 cm). Which solid is produced, and what are its dimensions?
A cylinder with radius 8 cm and height 3 cm
A cylinder with radius 3 cm and height 8 cm
A cylinder with radius 3 cm and height 3 cm
A cylinder with radius 8 cm and height 8 cm
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