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NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.2 β Part 2
Q-4 The diameter of a roller is and its length is . It takes complete revolutions to move once over to level a playground. Find the area of the playground in .
Solution:
- The roller length is (h)
- The cylinder radius is
- Total no. of revolutions
- Distance covered by roller in one revolution
- Area of the playground
- ( complete revolutions to level a playground)
Q-5 A cylindrical pillar is in diameter and in height. Find the cost of painting the curved surface of the pillar at the rate of .
Solution:
- The pillar radius
- The pillar height
- Painting rate
- Curved surface
- Total cost of painting
- (Painting rate )
- Curved surface
Q-6 Curved surface area of a right circular cylinder is . If the radius of the base of the cylinder is , find its height.
Solution:
- The radius of the base r and the height of the cylinder h.
- Area of a right circular cylinder is
Curved surface area
Q-7 The inner diameter of a circular well is . It is deep. Find
- Its inner curved surface area,
- The cost of plastering this curved surface at the rate of
Solution:
Circular well radius
The well depth
Plastering rate
- Curved surface
- Cost of plastering =
Q-8 In a hot water heating system, there is a cylindrical pipe of length and diameter . Find the total radiating surface in the system.
Solution:
- The pipe radius
- The pipe length
Total radial surface or curved surface area of the pipe