Page 74 - Mathematics Class - IX

Viva-Voce

1. How will you define a cone?
Ans. A cone is a three-dimensional geometrical shape that has one circular base and one vertex.

2. What is the sector of a circle?
Ans. The sector of a circle is the portion which is enclosed by two radii and an arc.
3. What is the formula for curved surface area of a cone?

Ans. Curved surface area of a cone = prl, where r = radius and l = slant height
4. How will you find the area of base of a cone?

Ans. The area of base of a cone can be calculated with help of the formula for finding the area of a circle, i.e. pr .
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5. What is the slant height of a cone?

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Ans. Slant height, l = h + r , where, r = radius and h = height
6. The diameter of the base of a cone is 10.5 cm and its slant height is 10 cm then find its curved surface area.

Ans. 165 sq. cm
7. What is the total surface area of cone of base radius ‘r’ and slant height ‘l’?

Ans. prl + pr 2

MCQs

1. The portion of the circle which is less than a semi-circle is called
a) major sector b) minor sector c) half sector d) semi sector

2. How many surface area a cone has?
a) 2 b) 1 c) 6 d) 8

3. The portion of the circle which is more than a semi-circle is called
a) major sector b) minor sector c) half sector d) semi sector
4. Find the curved surface area of the cone if radius of base is 7 cm and slant height is 9 cm.

a) 63 cm b) 154 cm c) 198 cm d) 298 cm 2
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5. Which of the following is used to find the area of the sector?
a) Arc length b) Area of the circle
c) Circumference of the circle d) All of these

Answers: 1. b) Minor sector 2. a) 2 3. a) Major sector

4. c) 198 cm 5. d) All of these
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