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Question

Find the volume (in cm³) of the largest right circular cone that can be cut out from a cube with an edge of 8 cm. Use $\pi = \frac{22}{7}$

The correct answer is
$134\frac{2}{21}$

Calculating the Volume of the Largest Cone from a Cube

The problem asks us to find the volume of the largest possible right circular cone that can be formed by cutting it from a cube with side length 8 cm. We are given the value of pi as $\frac{22}{7}$.

Understanding the Geometry

To cut the largest possible right circular cone from a cube:

  • The diameter of the cone's base must be equal to the edge length of the cube.
  • The height of the cone must also be equal to the edge length of the cube.

Identifying Dimensions

Given:

  • Edge length of the cube, denoted as '$a$' = 8 cm.

For the largest inscribed cone:

  • Diameter of the base ($d$) = $a$ = 8 cm.
  • Radius of the base ($r$) = $\frac{d}{2} = \frac{8 \text{ cm}}{2}$ = 4 cm.
  • Height of the cone ($h$) = $a$ = 8 cm.

Applying the Volume Formula

The formula for the volume ($V$) of a right circular cone is:

$$V = \frac{1}{3} \pi r^2 h$$

Step-by-Step Calculation

  1. Substitute the known values into the formula: $$V = \frac{1}{3} \times \frac{22}{7} \times (4 \text{ cm})^2 \times (8 \text{ cm})$$
  2. Calculate the square of the radius: $$(4 \text{ cm})^2 = 16 \text{ cm}^2$$
  3. Multiply the terms: $$V = \frac{1}{3} \times \frac{22}{7} \times 16 \text{ cm}^2 \times 8 \text{ cm}$$ $$V = \frac{1}{3} \times \frac{22}{7} \times 128 \text{ cm}^3$$
  4. Perform the multiplication: $$V = \frac{22 \times 128}{3 \times 7} \text{ cm}^3$$ $$V = \frac{2816}{21} \text{ cm}^3$$
  5. Convert the improper fraction to a mixed number: Divide 2816 by 21: $$2816 \div 21 = 134 \text{ with a remainder of } 2$$ So, the volume is $134\frac{2}{21}$ cm³.

Final Volume

The volume of the largest right circular cone that can be cut from the cube is $\frac{2816}{21}$ cm³, which is equal to $134\frac{2}{21}$ cm³.

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Important Questions from 3-D Mensuration

  1. Find the surface area of a sphere whose diameter is equal to 98 cm.
  2. A conical vessel has base radius 31 cm and height 45 cm. Water is poured into the vessel until it is $\frac{2}{3}$ full. Find the volume (in cm³) of water in the vessel.
  3. A solid metallic sphere of radius 10 cm is melted and recast into 125 identical spheres. What is the ratio of the surface area of the original sphere to the total surface area of 6 smaller spheres so formed?
  4. The volume of a solid cylinder is 5852 cm³ and its height is 38 cm. What is the total surface area of the solid cylinder? (Round your answer to the nearest integer) (Use $\pi = \frac{22}{7}$)
  5. Find the surface area of a sphere whose diameter is equal to 112 cm.
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