Question

A designer is creating a modern art sculpture of an hourglass out of steel, to be on display at the town library. The hourglass is made by two cones meeting at the top point. The designer wants to know how many square feet of steel is needed for the outside of the sculpture, if the slant height of each cone is 5 feet and the diameter is 8 feet. Use 3.14 for pi.

Answer 1

Each cone’s lateral area = π r l. Here r = 4 ft (diameter 8 ft) and l = 5 ft.

One cone: A = π(4)(5) = 20π. Two cones: 2×20π = 40π.

Using π = 3.14: 40×3.14 = 125.6

So 125.6 square feet of steel (assuming no base disks, since the cones meet at their tips).