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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

Volume is the measure of the amount of three-dimensional space occupied by an object. To visualize this, imagine the total amount of water required to completely fill a hollow 3D container; that quantity represents its volume.

The standard units for measuring volume are cubic units, such as cubic centimeters (cm3cm^3) or cubic meters (m3m^3). This is because volume is derived from the product of three linear dimensions (length, width, and height).

A cuboid is a solid bounded by six rectangular faces. To visualize its volume, consider a rectangular box with length ll, breadth bb, and height hh; the total space inside the box is the product of these three dimensions.

A cube is a specific type of cuboid where all edges are of equal length, denoted as aa. Visually, it looks like a standard die where the length, breadth, and height are identical, resulting in a volume of a×a×aa \times a \times a.

A cylinder consists of two congruent circular bases connected by a curved surface. To visualize its volume, imagine a stack of identical circular coins. The total volume is the area of the bottom circular base multiplied by the total height hh of the stack.

The general principle for finding the volume of any uniform solid (like a prism or cylinder) is multiplying the Area of the Base by the perpendicular Height. This is expressed as V=Area of Base×hV = \text{Area of Base} \times h.

Capacity refers to the volume of a substance (like liquid) that a container can hold. While volume measures the space an object occupies, capacity specifically measures the interior space of hollow objects, often measured in liters (LL) or milliliters (mlml).

Units of capacity are related to cubic units: 1000cm3=1 liter1000 cm^3 = 1 \text{ liter} and 1m3=1000 liters1 m^3 = 1000 \text{ liters}. Another useful conversion is 1cm3=1ml1 cm^3 = 1 ml.

📐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×h1.54=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.