Class 9 | Chapter 13 | Surface areas and Volumes | Exercise 13.2 | Question 9

Question 9: Find

  1. the lateral or curved surface area of a closed cylindrical petrol storage tank that is 4.2 m in diameter and 4.5 m high.
  2. how much steel was actually used, if 1/12 of the steel actually used was wasted in making the tank.

Prerequisite

A closed cylinder has 3 surfaces:

  • Curved or lateral surface 
  • Top 
  • Base

The formula to calculate the curved surface area and total surface area are quite simple to learn and derive.

Lateral or curved surface area of cylinder = 2πrh

r = radius, h = height (or length)

Total surface area of cylinder = 2πr ( r + h ) 

r = radius, h = height (or length)

It is recommended to understand the core concept of area, surface area and volume before we attempt any question based on these concepts.

 
Derivation of formula – Surface area of cylinder
 

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