NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.2 – Part 1 (For CBSE, ICSE, IAS, NET, NRA 2022)

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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
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

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

Solution:

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

  • Inner curved surface
  • Outer curved surface
  • ()
  • Total surface area of a pipe = Inner curved surface area + outer curved surface area + areas of two base
  • ()