NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.7 – Part 3
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Q6 The volume of a right circular cone is. If the diameter of the base is, find

Height of the cone

Slant height of the cone

Curved surface area of the cone
Solution:

Diameter of the base of the cone
Therefore radius ()
Let the height of the cone be

Now, volume of the cone =







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


Given,

Radius

Slant height
Therefore curved surface area
Q7 A right triangle with sides , and is revolved about the side. Find the volume of the solid so obtained.
Solution:
Note than when right triangle is revolved we get a cone with the same radius as the base of the right triangle.
Height is.
In triangle

Base is

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