Ex 11.3, 9
A heap of wheat is in the form of a cone whose diameter is 10.5 m and height is 3 m. Find its volume. The heap is to be covered by canvas to protect it from rain. Find the area of the canvas required.
Radius of cone = r = /2 = (10.5/2) m = 5.25 m
Height of the cone = h = 3 m
Volume of the cone (heap) = 1/3 r2h
= (1/3 22/7 5.25 5.25 3) m3
= 86.625 m3
We have to find area of canvas required,
i.e., curved surface area of cone
Curved Surface Area of cone = r
We know that
2 = h2 + r2
2 = 32 + (5.25)2
2 = 9 + 27.5625
2 = 36.5625
= 36.5625
= 6.046
Curved surface area of cone = r
= (22/7 5.25 6.046) m2
= 99.756 m2

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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