NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.3 – Part 3
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Surface Area and Volume of a Cone
Surface area and volume of a cone
Q-6 The slant height and base diameter of a conical tomb are and respectively. Find the cost of white-washing its curved surface at the rate of perSolution:
We know,
-
Base diameter =
-
Radius (r)
-
Slant height of tomb (l)
Therefore curved surface area =
Rate of white- washing 100 m2
Rate of white- washing 1 m2
Therefore, total cost of white-washing the tomb with area
Q-7 A joker’s cap is in the form of a right circular cone of base radius and height. Find the area of the sheet required to make such caps.Solution:
-
The cone radius (r)
-
The cone height (h)
Now, l be the slant height
Sheet required for one cap = Curved surface of the cone
Sheet required for
Q-8 A bus stop is barricaded from the remaining part of the road, by using hollow cones made of recycled cardboard. Each cone has a base diameter of and height 1 m. If the outer side of each of the cones is to be painted and the cost of painting is , what will be the cost of painting all these cones? (Use and take)
Solution:
We are given,
-
Radius of the cone (r)
-
Height of the cone (h)
Now, the slant height of a cone is given by
We know that, rate of painting
Curved surface area of 1 cone =
Therefore, curved surface of such 50 cones =
Finally, cost of painting all these cones is (since, the cost of painting is )