How to find the surface area of a sphere

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Math › How to find the surface area of a sphere

Questions 1 - 10

In terms of $\pi$ , give the surface area, in square inches, of a spherical water tank with a diameter of 20 feet.

$57,600 \pi\textrm{ in}^{2}$

$2,304,000 \pi \textrm{ in}^{2}$

$18,432,000\pi\textrm{ in}^{2}$

$230,400 \pi\textrm{ in}^{2}$

$307,200\pi\textrm{ in}^{2}$

Explanation

feet = $20 \times 12 = 240$ inches, the diameter of the tank; half of this, or 120 inches, is the radius. Set , substitute in the surface area formula, and solve for :

$A =4\pi r^{2}$

$A =4\pi \cdot 120^{2}$

$A =4\pi \cdot 14,400$

$A = 57,600 \pi$

If the radius of the sphere is one half, what is the surface area?

$\pi$

$\frac{1}{4}\pi$

$\frac{1}{2}\pi$

$\frac{4}{3}\pi$

$2\pi$

Explanation

Write the formula for the surface area of a sphere, plug in the radius, and find the area.

$A=4\pi r^2 = 4\pi \left(\frac{1}{2}\right)^2 = 4\pi\left(\frac{1}{4}\right)= \pi$

Find the surface area of a sphere if the volume is .

$4\pi\left(\frac{3}{4\pi}\right)^\frac{2}{3}$

$\sqrt[3]{9}$

$4\pi\left(\frac{4}{3\pi}\right)^\frac{2}{3}$

$\left(\frac{3}{4\pi}\right)^\frac{2}{3}$

$\sqrt[3]{\frac{3\pi}{4}}$

Explanation

Write the formula for the volume of a sphere and substitute volume to find radius.

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

$1=\frac{4}{3}\pi r^3$

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

$r=\sqrt[3]{\frac{3}{4\pi}}= (\frac{3}{4\pi})^\frac{1}{3}$

Write the formula for the surface area of a sphere and plug in the radius.

$A=4\pi r^2 = 4\pi \left[\left(\frac{3}{4\pi}\right)^\frac{1}{3}\right]^2 = 4\pi\left(\frac{3}{4\pi}\right)^\frac{2}{3}$

Find the surface area of a hemisphere that has a radius of $\frac{3}{2}$ .

Explanation

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

$\text{Surface Area of Sphere}=4\pi r^2$ , where is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

$\text{Area of Circle}=\pi r^2$

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

$\text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2$

Plug in the given radius to find the surface area.

$\text{Surface Area of Hemisphere}=3\pi (\frac{3}{2})^2=21.21$

Make sure to round to places after the decimal.

Find the surface area of a hemisphere that has a radius of .

Explanation

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

$\text{Surface Area of Sphere}=4\pi r^2$ , where is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

$\text{Area of Circle}=\pi r^2$

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

$\text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2$

Plug in the given radius to find the surface area.

$\text{Surface Area of Hemisphere}=3\pi (3)^2=84.82$

Make sure to round to places after the decimal.

If the radius of a sphere is , what is the sphere's surface area?

$4\pi:units$

$8\pi:units$

$\frac{4}{3}\pi:units$

$\frac{16}{9}\pi:units$

$2\pi:units$

Explanation

Write the formula for surface area of a sphere:

$A=4\pi r^2$

Plug in the value of radius and solve for the surface area:

$A=4\pi (1)^2 = 4\pi$

If the radius of a sphere is , what is the surface area of the sphere?

$900\pi$

$225\pi$

$675\pi$

$13500\pi$

$300\pi$

Explanation

Write the equation for the surface area of a sphere.

$A=4\pi r^2$

Substitute the radius and find the area.

$A=4\pi (15)^2 = 4\pi(225)=900\pi$

Find the surface area of a hemisphere with a radius of .

Explanation

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

$\text{Surface Area of Sphere}=4\pi r^2$ , where is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

$\text{Area of Circle}=\pi r^2$

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

$\text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2$

Plug in the given radius to find the surface area.

$\text{Surface Area of Hemisphere}=3\pi (11)^2=1140.40$

Make sure to round to places after the decimal.

If the diameter of a sphere is , what is the surface area?

$225\pi$

$900\pi$

$42\pi$

$500\pi$

$56.25\pi$

Explanation

The radius is half the length of a diameter.

$r=\frac{d}{2}=\frac{15}{2}=7.5$

Write the formula for the surface area of a sphere and plug in the radius.

$A=4\pi r^2 = 4\pi(7.5)^2= 225\pi$

Find the surface area of a hemisphere with a radius of .

Explanation

In order to find the area of a hemisphere, which is just half a sphere, you will need to first find half the surface area of the sphere.

Recall how to find the surface area of a sphere:

$\text{Surface Area of Sphere}=4\pi r^2$ , where is the radius.

Now, since the sphere is cut in half, it also has a circle as its base.

Recall how to find the area of a circle:

$\text{Area of Circle}=\pi r^2$

Now add together half the surface area of a sphere with the area of the circular base to find the surface area of a hemisphere.

$\text{Surface Area of Hemisphere}=2\pi r^2+\pi r^2=3 \pi r^2$

Plug in the given radius to find the surface area.

$\text{Surface Area of Hemisphere}=3\pi (8)^2=603.19$

Make sure to round to places after the decimal.

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