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Mensuration - Volume of Cube, Cuboid, and Cylinder

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Volume refers to the amount of space occupied by a three-dimensional object. For a cuboid, it is calculated as the product of its length (ll), breadth (bb), and height (hh).

3D cuboid showing length, breadth, and height
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A cube is a special case of a cuboid where all edges are equal in length (aa). The volume is given by V=a×a×a=a3V = a \times a \times a = a^3.

3D cube with equal side length a
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The volume of a cylinder is the product of the area of its circular base and its height (hh). If the radius of the base is rr, Volume V=Area of base×h=πr2hV = \text{Area of base} \times h = \pi r^2 h.

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Capacity is the volume of substance that a container can hold. Common units include cm3cm^3, m3m^3, and Litres (LL).

📐Formulae

Volume of a Cuboid: V=l×b×hV = l \times b \times h

Volume of a Cube: V=a3V = a^3

Volume of a Cylinder: V=πr2hV = \pi r^2 h

Base Area of a Cylinder: A=πr2A = \pi r^2

Capacity Conversion: 1L=1000cm31 L = 1000 cm^3

Capacity Conversion: 1m3=1,000,000cm3=1000L1 m^3 = 1,000,000 cm^3 = 1000 L

💡Examples

Problem 1:

A cuboidal water tank is 6m6 m long, 5m5 m wide, and 4.5m4.5 m deep. How many liters of water can it hold?

Solution:

Step 1: Identify the given dimensions: length l=6ml = 6 m, breadth b=5mb = 5 m, and height h=4.5mh = 4.5 m. Step 2: Use the formula for the volume of a cuboid: V=l×b×hV = l \times b \times h. Step 3: Substitute the values: V=6×5×4.5=135m3V = 6 \times 5 \times 4.5 = 135 m^3. Step 4: Convert the volume from cubic meters to liters. We know that 1m3=1000L1 m^3 = 1000 L. Step 5: Total capacity in liters = 135×1000=135,000L135 \times 1000 = 135,000 L.

Explanation:

To find the capacity, we first calculate the volume in cubic meters by multiplying the length, width, and depth, then convert the result to liters using the standard conversion factor.

Problem 2:

Find the height of a cylinder whose volume is 1.54m31.54 m^3 and the diameter of the base is 140cm140 cm.

Solution:

Step 1: Convert all units to meters. Volume V=1.54m3V = 1.54 m^3. Diameter d=140cm=1.4md = 140 cm = 1.4 m. Radius r=d2=1.42=0.7mr = \frac{d}{2} = \frac{1.4}{2} = 0.7 m. Step 2: Use the formula for the volume of a cylinder: V=πr2hV = \pi r^2 h. Step 3: Substitute the known values (π=227\pi = \frac{22}{7}): 1.54=227×(0.7)2×h1.54 = \frac{22}{7} \times (0.7)^2 \times h. Step 4: Simplify the expression: 1.54=227×0.49×h1.54 = \frac{22}{7} \times 0.49 \times h. Step 5: Further simplify: 1.54=22×0.07×h⇒1.54=1.54×h1.54 = 22 \times 0.07 \times h \Rightarrow 1.54 = 1.54 \times h. Step 6: Solve for hh: h=1.541.54=1mh = \frac{1.54}{1.54} = 1 m.

Explanation:

The problem requires finding the height given volume and diameter. Consistency in units is key, so we converted centimeters to meters before applying the volume formula for a cylinder.

Problem 3:

Three metallic cubes with edges 3cm3 cm, 4cm4 cm, and 5cm5 cm are melted to form a single large cube. Find the edge of the new cube.

Three small cubes merging into one larger cube

Solution:

Volume of first cube V1=33=27cm3V_1 = 3^3 = 27 cm^3 Volume of second cube V2=43=64cm3V_2 = 4^3 = 64 cm^3 Volume of third cube V3=53=125cm3V_3 = 5^3 = 125 cm^3 Total volume of new cube V=V1+V2+V3V = V_1 + V_2 + V_3 V=27+64+125=216cm3V = 27 + 64 + 125 = 216 cm^3 Let the edge of the new cube be AA. A3=216A^3 = 216 A=2163=6cmA = \sqrt[3]{216} = 6 cm

Explanation:

Since the cubes are melted and recast, the total volume remains conserved. We calculate the volumes of the three smaller cubes, sum them up to find the volume of the large cube, and then find its cube root to determine the edge length.

Problem 4:

A cylindrical pillar has a radius of 14 cm14\text{ cm} and a height of 3 m3\text{ m}. Find the volume of the pillar in cubic centimeters. Also, if the cost of painting the curved surface is Rs 10Rs\text{ }10 per 100 cm2100\text{ cm}^2, find the cost of painting 55 such pillars (Note: Focus on volume calculation first).

A cylinder representing a pillar with radius 14 cm and height 3 m.

Solution:

Radius (r)=14 cm\text{Radius (r)} = 14\text{ cm} Height (h)=3 m=300 cm\text{Height (h)} = 3\text{ m} = 300\text{ cm} Volume of one cylinder=πr2h\text{Volume of one cylinder} = \pi r^2 h Volume=227×14×14×300\text{Volume} = \frac{22}{7} \times 14 \times 14 \times 300 Volume=22×2×14×300\text{Volume} = 22 \times 2 \times 14 \times 300 Volume=44×4200\text{Volume} = 44 \times 4200 Volume=184800 cm3\text{Volume} = 184800\text{ cm}^3

Explanation:

To find the volume of a cylinder, we use the formula V=πr2hV = \pi r^2 h. First, ensure all units are consistent by converting the height from meters to centimeters (1 m=100 cm1\text{ m} = 100\text{ cm}). Substituting the values r=14r = 14 and h=300h = 300 into the formula allows us to calculate the space occupied by the pillar.

Volume of Cube, Cuboid, and Cylinder Class 8 Notes & Examples