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

Surface area of cone=πrl

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,

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