NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.2 – Part 1

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Q-1 The curved surface area of a right circular cylinder of height is . Find the diameter of the base of the cylinder.

A rectangle rolled into a cylinder

Curved Surface of a Cylinder Made From a Rectangle

A rectangle rolled into a cylinder

Understanding curved surface area of a cylinder.

Curved Surface Area of a Cylinder as the Area of a Rectangle

Understanding curved surface area of a cylinder.

Solution:

The radius of the base is and the height of the cylinder. Therefore, curved surface area of cylinder

  • (Given)

So, the diameter of the base is =

Q-2 It is required to make a closed cylindrical tank of height 1 m and base diameter 140 cm from a metal sheet. How many square metres of the sheet are required for the same?Solution:

Total surface area of a cylinder

Total Surface Area of Cylinder

Total surface area of a cylinder

We are given that diameter of base and Height

Therefore, metal sheet required to make a closed cylindrical tank =

Q-3 A metal pipe is long. The inner diameter of a cross section is , the outer diameter being (see Fig.). Find its

  1. Inner curved surface area,

  2. Outer curved surface area,

  3. Total surface area.

a Metal Pipe

A metal pipe is 77cm long, Inner diameter is4cm, outer diameter is 4.4cm

Solution:

External radius is and the internal radius is the length of the pipe is , therefore

  1. Inner curved surface

  2. Outer curved surface

    • ( )

  3. Total surface area of a pipe = Inner curved surface area + outer curved surface area + areas of two base

  • ( )

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