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

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Surface area of cone=πrl

Lateral Surface Area of Cone

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Slant height l or s =

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

  1. Slant height of the tent.

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

Solution(I):

  • Radius of the base (r)

  • Height of the conical tent (h)

Therefore, the slant height of the cone is.

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 canvas

Area of canvas = ()

Therefore, cost of canvas = Rs.

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

  • Radius of the base (r)

  • Height of the conical tent (h)

Now, l is the slant height of the cone

Curved surface area of conical tent =

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

That is,