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MP Board · Class 10 · Mathematics · Surface Areas and VolumesExplain in detail the mathematical concepts and derivation steps involved in finding the total surface area and volume of a frustum of a cone. Include appropriate formulas and clearly label all parameters.

Step-by-Step Solution

Introduction to Frustum of a Cone\nWhen a right circular cone is cut by a plane parallel to its base, the portion remaining between the cutting plane and the base is called a frustum of a cone. It has two circular bases of different radii and a curved surface.

Parameters of a Frustum\nLet the radius of the top circular base be $r_1$, the radius of the bottom circular base be $r_2$ (where $r_2 > r_1$), the vertical height of the frustum be $h$, and the slant height be $l$.

1. Slant Height of the Frustum ($l$)\nUsing the Pythagorean theorem in the cross-section containing the axis of the frustum:

$$l = \sqrt{h^2 + (r_2 - r_1)^2}$$

2. Curved Surface Area (CSA)\nThe curved surface area is obtained by considering it as the difference between two similar cones. The formula is:

$$\text{CSA} = \pi (r_1 + r_2) l$$

3. Total Surface Area (TSA)\nTo find the total surface area, we add the areas of both circular bases (top and bottom) to the curved surface area:

$$\text{TSA} = \pi (r_1 + r_2) l + \pi r_1^2 + \pi r_2^2$$

4. Volume of the Frustum ($V$)\nThe volume is derived from the difference of volumes of two complete cones. The standard formula is:

$$V = \frac{1}{3} \pi h (r_1^2 + r_2^2 + r_1 r_2)$$

Summary of Applications\nFrustums are widely observed in everyday objects such as buckets, drinking glasses, and funnel shapes. Understanding these formulas helps in solving complex industrial and architectural mensuration problems efficiently.

💡 Study Guide: This question tests core syllabus concepts from Surface Areas and Volumes. For formulas, key summaries, and mock exam reference guides, read the full Surface Areas and Volumes Revision Notes.
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