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The sphere and cylinder have the same radius and height. The volume of the cylinder is [tex]18 \, m^3[/tex]. What is the volume of the sphere?

A. [tex]12 \, m^3[/tex]
B. [tex]15 \, m^3[/tex]
C. [tex]18 \, m^3[/tex]
D. [tex]27 \, m^3[/tex]

Sagot :

To find the volume of a sphere given that it has the same radius and height (which is equal to the diameter) as the cylinder, we can follow these steps:

Step 1: Understand the relationship between the cylinder and the sphere.
- The cylinder has a volume [tex]\( V_{\text{cylinder}} = 18 \, m^3 \)[/tex].
- The volume of a cylinder is given by the formula [tex]\( V = \pi r^2 h \)[/tex].
- The height of the cylinder is double the radius (since the height of the cylinder equals the diameter of the sphere), so we can write [tex]\( h = 2r \)[/tex].

Step 2: Express the volume of the cylinder in terms of the radius.
- Using the cylinder's volume formula and the relationship [tex]\( h = 2r \)[/tex], we get:
[tex]\[ V_{\text{cylinder}} = \pi r^2 \cdot 2r = 2\pi r^3 \][/tex]
- We know [tex]\( V_{\text{cylinder}} = 18 \, m^3 \)[/tex], so:
[tex]\[ 18 = 2\pi r^3 \][/tex]

Step 3: Solve for the radius [tex]\( r \)[/tex].
- Rearrange the equation to isolate [tex]\( r^3 \)[/tex]:
[tex]\[ r^3 = \frac{18}{2\pi} \][/tex]
[tex]\[ r^3 = \frac{9}{\pi} \][/tex]

Step 4: Calculate the radius cubed.
- The specific value is:
[tex]\[ r^3 \approx 2.8648 \][/tex]

Step 5: Find the volume of the sphere.
- The volume of a sphere is given by [tex]\( V = \frac{4}{3} \pi r^3 \)[/tex].
- Substitute [tex]\( r^3 \)[/tex]:
[tex]\[ V_{\text{sphere}} = \frac{4}{3} \pi \cdot \frac{9}{\pi} \][/tex]
- Simplify the expression:
[tex]\[ V_{\text{sphere}} = \frac{4}{3} \cdot 9 \][/tex]
[tex]\[ V_{\text{sphere}} = 12 \, m^3 \][/tex]

Therefore, the volume of the sphere is [tex]\( 12 \, m^3 \)[/tex].