NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.7 – Part 3

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Cone volume=1/3 πr^2 h

Cone Volume

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Q-6 The volume of a right circular cone is. If the diameter of the base is, find

  1. Height of the cone

  2. Slant height of the cone

  3. Curved surface area of the cone


I. Diameter of the base of the cone

Therefore radius ()

Let the height of the cone be

  • Now, volume of the cone =

II. Radius , Height , Let the slant height of the cone be , than

III. Given,

  • Radius

  • Slant height

Therefore curved surface area

Q-7 A right triangle with sides , and is revolved about the side. Find the volume of the solid so obtained.


Note than when right triangle is revolved we get a cone with the same radius as the base of the right triangle.

When a right triangle is rotated its base becomes the radius …

Cone Formed by Rotating Right Triangle

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Triangle BEC

Height is.

In triangle

  • Base is

  • Height is.

Cone so obtained has radius r = 5 cm and height 12 cm. Its volume,