Question

A sphere and a cylinder have the same radius and height. The volume of the cylinder is 21m. what is the volume of the sphere.​

Answer 1

Answer:

The volume of the sphere is 14m³

Step-by-step explanation:

Given

Volume of the cylinder = $21m^3$

Required

Volume of the sphere

Given that the volume of the cylinder is 21, the first step is to solve for the radius of the cylinder;

Using the volume formula of a cylinder

The formula goes thus

$V = \pi r^2h$

Substitute 21 for V; this gives

$21 = \pi r^2h$

Divide both sides by h

$\frac{21}{h} = \frac{\pi r^2h}{h}$

$\frac{21}{h} = \pi r^2$

The next step is to solve for the volume of the sphere using the following formula;

$V = \frac{4}{3}\pi r^3$

Divide both sides by r

$\frac{V}{r} = \frac{4}{3r}\pi r^3$

Expand Expression

$\frac{V}{r} = \frac{4}{3}\pi r^2$

Substitute $\frac{21}{h} = \pi r^2$

$\frac{V}{r} = \frac{4}{3} * \frac{21}{h}$

$\frac{V}{r} = \frac{84}{3h}$

$\frac{V}{r} = \frac{28}{h}$

Multiply both sided by r

$r * \frac{V}{r} = \frac{28}{h} * r$

$V = \frac{28r}{h}$ ------ equation 1

From the question, we were given that the height of the cylinder and the sphere have equal value;

This implies that the height of the cylinder equals the diameter of the sphere. In other words

$h = D$ , where D represents diameter of the sphere

Recall that $D = 2r$

So, $h = D = 2r$

$h = 2r$

Substitute 2r for h in equation 1

$V = \frac{28r}{2r}$

$V = \frac{28}{2}$

$V = 14$

Hence, the volume of the sphere is 14m³

Answer 2

Answer:

14 m³

Step-by-step explanation:

We have:

$Cylinder:\\\R-\text{radius}\\H=2R-\text{height}\\V_C-\text{volume};\ V_C=21m^3\\\\\text{the formula of a volume of a cylinder:}\ V=\pi R^2H\\\\V_C=\pi R^2(2R)=2\pi R^3$

$Sphere:\\\R-\text{radius}\\V_S-\text{volume}\\\\\text{the formula of a volume of a sphere:}\ V=\dfrac{4}{3}\pi R^3$

$Let's\ transform\ V_C:\\\\2\pi R^3=21\qquad\text{divide both sides by 2}\\\\\pi R^3=\dfrac{21}{2}\qquad\text{multiply both sides by}\ \dfrac{4}{3}\\\\\dfrac{4}{3}\pi R^3=\dfrac{21}{2}\cdot\dfrac{4}{3}\to V_S=\dfrac{(21:3)\cdot(4:2)}{(2:2)\cdot(3:3)}=\dfrac{7\cdot2}{1\cdot1}=\dfrac{14}{1}=14\ (m^3)$