Example exercise: volume and surface area of a cube
We have a cube whose length is 2 cm and we are asked to find its volume and surface area.
Finding the volume of a cube
The volume of a cube is equal to length × width × height.
Since the length, width and height of a cube are all equal, in our case the width and height of our given cube will also be 2 cm. Therefore,
8=2×2×2
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Test your knowledge
Question 1
Given the cube
How many edges are there in the cube?
Incorrect
Correct Answer:
\( 12 \)
Question 2
A cube has edges measuring 3 cm.
What is the volume of the cube?
Incorrect
Correct Answer:
\( 27 \)
Question 3
Look at the cube below.
Do all cubes have 6 faces, equaling its surface area?
Incorrect
Correct Answer:
Yes.
Finding the surface area of a cube
To find the total surface area of a cube, we will first find the surface area of one of its faces and then multiply the result by 6 (remember that cubes are composed of six identical square faces).
The area of each square is 4=2×2
Therefore, the surface area of the cube will be:
4×6=24cm
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Example exercises
Example exercise 1
Given that:
The length of each side of the given cube is equal to 3 cm.
Question:
What is the volume of the cube?
Solution:
The volume of a cube (and the volume of a cuboid) is equal to:
Length × Width × Height
Therefore the volume of the cube: =33=27
Answer:
27cm3
Do you know what the answer is?
Question 1
A cube has a total of 14 edges.
Incorrect
Correct Answer:
False.
Question 2
Given the cube whose edge length is equal to 7 cm
What is the sum of the lengths of the edges of the cube?
Incorrect
Correct Answer:
\( 84 \)
Question 3
Shown below is a cube with a length of 4 cm.
What is the sum of the lengths of the cube's edges?
Incorrect
Correct Answer:
\( 48 \)
Example exercise 2
Given that:
Given a cube in which each face has a surface area of 6 cm.
Assignment:
What is the total surface area of the cube?
Solution:
The total surface area of the cube is the combined area of all of its faces, ie:
Face area
6×6=36
Answer:
36cm2
Example exercise 3
Given that:
In the given cube, the length of each edge is equal to 3 cm.
Question:
What is the length of the diagonal of the face?
Solution:
To solve this question we will use the Pythagorean Theorem to find the length of the diagonal of the face:
A2+B2=C2
Or, in our case:
Edge2+Edge2=Diagonal2
=32+32
=18
18=3×2=diagonal
Answer:
32
Check your understanding
Question 1
The cube shown below has a base area of 16 cm².
Is it possible to calculate the height of the cube? If so, what is it?
Incorrect
Correct Answer:
\( 4 \)
Question 2
A cube has a base area of 9 cm².
Is it possible to calculate the volume of the cube? If so, what is it?
Incorrect
Correct Answer:
\( 27 \)
Question 3
Given the cube and the length of each edge equals 6.5 cm
What is the sum of the lengths of the edges of the cube?
Incorrect
Correct Answer:
\( 78 \)
Example exercise 4
Given a cube whose edge length is equal to 5 cm.
Task:
Find the volume of the cube.
Solution:
The volume of the cube is equal to the length of the face of the cube to the power of 3
We can write it like this:
53=125
Answer:
125cm3
Example exercise 5
Given a cube whose volume is equal to 112 cm³
Question:
How many whole cubes with a volume of 10 cm³ can fit inside the given cube?
Solution:
We divide the volume of the large cube into 10 to find out how many cubes of 10 cm³ fit into the given cube:
10112=1151
Since we are only asked about whole cubes, it is possible to enter 11 cubes into the cube whose volume is 112 cm³.
Answer:
11 cubes.
Do you think you will be able to solve it?
Question 1
The cube shown below has a base area equal to 36 cm².
Is it possible to calculate the height of the cube? If so, what is it?
Incorrect
Correct Answer:
\( 6 \)
Question 2
All faces of the cube must be?
Incorrect
Correct Answer:
Squares
Question 3
Find a,b
Incorrect
Correct Answer:
\( a=b=5 \)
Review questions
What is a cube?
A cube is a cuboid with six square, equal faces (all the sides are equal).
How do we find the surface area of a cube?
To find the total surface area of a cube, all we need is the value of one of its sides (since all sides are equal).
Then, we find the surface area of one face by multiplying the side to the power of three.
Lastly, we multiply the surface area of one face by six (since cubes have six equal sides).
Example exercise
Task. Find the total surface area of the following given cube, which has a side length of 7cm
Solution:
Let's start by finding the area of just one face:
Area=7cm×7cm=49cm2
Now, let's multiply the area of one face by six to find the total surface area:
49cm2×6=294cm2
Answer:
=294cm2
Test your knowledge
Question 1
Which of the following figures represents an unfolded cube?
Incorrect
Correct Answer:
Question 2
The surface area of a cube is 24 cm².
How long are the sides of the cube?
Incorrect
Correct Answer:
2
Question 3
How many faces does a cube have?
Incorrect
Correct Answer:
\( 6 \)
What is the formula used to find the volume of a cube?
The find the volume of a cube, we multiply its three sides.
Remember: since each face is square, all its sides have the same length.
=,×
This formula can also be expressed as:
V=L3
since all the sides are equal.
Finding the volume of a cube: additional practice
Example 1
Task. Find the volume of a cube with a side length of4cm
Solution:
Using our formula, we get:
V=L3
V=(4cm)3=64cm3
Answer
V=64cm3
Example 2
Task. Find the volume of a cube with a side length of 8cm
Solution:
Again, we will use our formula to find the volume:
V=L3
V=(8cm)3=512cm3
Answer
V=512cm3
Do you know what the answer is?
Question 1
Given the cube
How many edges are there in the cube?
Incorrect
Correct Answer:
\( 12 \)
Question 2
A cube has edges measuring 3 cm.
What is the volume of the cube?
Incorrect
Correct Answer:
\( 27 \)
Question 3
Look at the cube below.
Do all cubes have 6 faces, equaling its surface area?
Incorrect
Correct Answer:
Yes.
Examples with solutions for Cubes
Exercise #1
If we increase the side of a cube by 6, how many times will the volume of the cube increase by?
Video Solution
Step-by-Step Solution
Let's denote the initial cube's edge length as x,
The formula for the volume of a cube with edge length b is:
V=b3
Therefore the volume of the initial cube (meaning before increasing its edge) is:
V1=x3
Proceed to increase the cube's edge by a factor of 6, meaning the edge length is now: 6x . Therefore the volume of the new cube is:
V2=(6x)3=63x3
In the second step we simplified the expression for the new cube's volume by using the power rule for multiplication in parentheses:
(z⋅y)n=zn⋅yn
We applied the power to each term inside of the parentheses multiplication.
Next we'll answer the question that was asked - "By what factor did the cube's volume increase", meaning - by what factor do we multiply the old cube's volume (before increasing its edge) to obtain the new cube's volume?
Therefore to answer this question we simply divide the new cube's volume by the old cube's volume:
V1V2=x363x3=63
In the first step we substituted the expressions for the volumes of the old and new cubes that we obtained above. In the second step we reduced the common factor between the numerator and denominator,
Therefore we understood that the cube's volume increased by a factor of -63when we increased its edge by a factor of 6,
The correct answer is b.
Answer
63
Exercise #2
How many faces does a cube have?
Video Solution
Answer
6
Exercise #3
Given the cube
How many edges are there in the cube?
Video Solution
Answer
12
Exercise #4
A cube has edges measuring 3 cm.
What is the volume of the cube?
Video Solution
Answer
27
Exercise #5
Look at the cube below.
Do all cubes have 6 faces, equaling its surface area?