NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.3 – Part 2

Surface area of cone=πrl

Lateral Surface Area of Cone

Surface area of cone=πrl

Slant height l or s = Equation

Q-4 A conical tent is Equation high and the radius of its base is Equation . Find

  1. Slant height of the tent.

  2. Cost of the canvas required to make the tent, if the cost of Equation canvas is Equation

Solution(I):

  • Radius of the base (r) Equation

  • Height of the conical tent (h) Equation

Therefore, the slant height of the cone is Equation .

  • Equation

  • Equation

  • Equation

  • Equation

  • Equation

  • Equation

Solution(II):

Canvas required to make the conical tent is the curved or lateral surface of the cone. Note that the tent does not have a base. Also, cost of Equation canvas Equation

Area of canvas = Equation ( Equation ) Equation

Therefore, cost of canvas = Equation Rs. Equation

5. What length of tarpaulin Equation wide will be required to make conical tent of height Equation and base radius Equation ? Assume that the extra length of material that will be required for stitching margins and wastage in cutting is approximately Equation (Use Equation ).Solution:

  • Radius of the base (r) Equation

  • Height of the conical tent (h) Equation

Now, l is the slant height of the cone Equation

Curved surface area of conical tent = Equation

We know that breadth of tarpaulin Equation . Let, Equation is length of tarpaulin sheet required of which we know from the problem that Equation will be wasted in cutting. So, the actual length used will be Equation . Now area of this sheet with length Equation and breadth of 3m must match the lateral surface area of the sheet,

That is, Equation

  • Equation

  • Equation

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