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Mensuration - Volume of Cube, Cuboid, and Cylinder

Grade 8ICSE

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

🔑Concepts

Volume is defined as the total three-dimensional space occupied by a solid object. It is measured in cubic units such as cm3cm^3 or m3m^3. Visually, you can imagine volume as the number of unit cubes that can fit perfectly inside a container without overlapping.

A Cube is a regular solid with six equal square faces. Every edge has the same length, denoted as aa. Visually, a cube looks like a perfectly symmetrical die where the length, breadth, and height are all equal, creating a uniform 3D shape.

A Cuboid is a solid with six rectangular faces. It is defined by three dimensions: length (ll), breadth (bb), and height (hh). Visually, it resembles a shoebox or a brick where the perpendicular edges meet at right angles, but the sides are not necessarily equal.

A Cylinder consists of two identical circular bases connected by a curved surface. The dimensions involved are the radius (rr) of the circular base and the vertical height (hh). Visually, it looks like a soda can or a section of a pipe, where the cross-section remains a constant circle throughout its height.

The general principle for finding the volume of right prisms (like cubes, cuboids, and cylinders) is multiplying the Area of the Base by the Height. For a cylinder, the circular base area is πr2\pi r^2, and for a cuboid, the rectangular base area is l×bl \times b.

Capacity refers to the volume of liquid or gas a hollow object can hold. The relationship between volume and capacity is crucial: 1 cm3=1 ml1 \text{ cm}^3 = 1 \text{ ml} and 1000 cm3=1 litre1000 \text{ cm}^3 = 1 \text{ litre}. Visually, imagine a 10 cm×10 cm×10 cm10 \text{ cm} \times 10 \text{ cm} \times 10 \text{ cm} cube filling exactly a 1-litre bottle.

Unit conversion is essential in volume calculations. To convert m3m^3 to cm3cm^3, multiply by 10,00,00010,00,000 (since 1 m=100 cm1 \text{ m} = 100 \text{ cm}, then 1 m3=1003 cm31 \text{ m}^3 = 100^3 \text{ cm}^3). Always ensure all dimensions are in the same units before calculating.

📐Formulae

Volume of a Cube=a3 (where a is the side length)\text{Volume of a Cube} = a^3 \text{ (where } a \text{ is the side length)}

Volume of a Cuboid=l×b×h\text{Volume of a Cuboid} = l \times b \times h

Volume of a Cylinder=πr2h\text{Volume of a Cylinder} = \pi r^2 h

Base Area of a Cylinder=πr2\text{Base Area of a Cylinder} = \pi r^2

Radius (r)=Diameter2\text{Radius } (r) = \frac{\text{Diameter}}{2}

1 Litre=1000 cm31 \text{ Litre} = 1000 \text{ cm}^3

1 m3=1000 Litres1 \text{ m}^3 = 1000 \text{ Litres}

💡Examples

Problem 1:

Find the volume of a cylinder with a base radius of 7 cm7 \text{ cm} and a height of 10 cm10 \text{ cm}. (Use π=227\pi = \frac{22}{7})

Solution:

  1. Identify given values: r=7 cmr = 7 \text{ cm}, h=10 cmh = 10 \text{ cm}.
  2. Use the formula: V=πr2hV = \pi r^2 h.
  3. Substitute the values: V=227×7×7×10V = \frac{22}{7} \times 7 \times 7 \times 10.
  4. Cancel out 77 from numerator and denominator: V=22×7×10V = 22 \times 7 \times 10.
  5. Calculate the final product: V=154×10=1540 cm3V = 154 \times 10 = 1540 \text{ cm}^3.

Explanation:

To find the cylinder's volume, we calculate the area of the circular base first using πr2\pi r^2 and then multiply it by the height. Substituting the radius and height into the formula gives the total space occupied in cubic centimeters.

Problem 2:

A cuboidal water tank is 5 m5 \text{ m} long, 4 m4 \text{ m} wide, and 3 m3 \text{ m} deep. Find its capacity in litres.

Solution:

  1. Calculate volume in cubic meters: V=l×b×h=5×4×3=60 m3V = l \times b \times h = 5 \times 4 \times 3 = 60 \text{ m}^3.
  2. Convert m3m^3 to litres: Since 1 m3=1000 litres1 \text{ m}^3 = 1000 \text{ litres}.
  3. Capacity = 60×1000=60,000 litres60 \times 1000 = 60,000 \text{ litres}.

Explanation:

We first find the volume of the tank by multiplying length, breadth, and depth. Since the question asks for capacity in litres, we use the conversion factor where 11 cubic meter equals 10001000 litres.