Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
8. Surface Areas and Volumes of Spheres
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Exercise 25 Page 653

Use the formula for volume of a sphere to find the volume of the hemisphere.

74003π ≈ 7749.26 cm^3

Practice makes perfect

We want to find the volume of a composite solid in the shape of a cylinder with a hemisphere attached to it.

Cylinder with a hemisphere attached to it.

We will first find the volume of the cylinder and then the volume of the hemisphere. Then we can add the results to find the volume of the solid. Let's do it!

Volume of the Cylinder

Let's begin by finding the volume of the cylinder.

Cylinder with a hemisphere attached to it. The cylinder is highlighted.
The volume of a cylinder is the product of the area of the base and the height. V= Bh Our cylinder has a circular base, B, and its area is the product of π times the radius squared. V= Bh ⇒ V = π r^2 h Let's substitute the corresponding values into the formula and find its volume.
V = π r^2 h
V = π ( 10)^2 ( 18)
Simplify right-hand side
V = π (100) (18)
V = π (1800)
V = 1800π
The cylinder has a volume of 1800π cm^3.

Volume of the Hemispere

The left section of the composite solid is in the shape of a hemisphere.

Cylinder with a hemisphere attached to it. The hemisphere is highlighted.
The volume of a hemisphere is half the volume of a sphere. V=43π r^3/2 ⇒ V = 2/3π r^3 We can now find the volume our hemisphere, which has a radius of 10 centimeters.
V = 2/3π r^3
V = 2/3π ( 10)^3
Simplify right-hand side
V = 2/3π (1000)
V = 2/3(1000)π
V = 2(1000)/3π
V= 2000/3π
The hemisphere has a volume of 20003πcm^3.

Volume of the Solid

To find the volume of the composite solid we will use the Volume Addition Postulate.

The volume of a solid is the sum of the volumes of all its non-overlapping parts.

The solid has two non-overlapping parts, one cylinder and one hemisphere. Let's add their volumes. V_(solid)= V_(cylinder)+ V_(hemisphere) ⇓ V_(solid)= 1800π+ 2000/3π = 7400/3π The solid has the volume 74003π ≈ 7749.26 cm^3.