Example 8 - Chapter 11 Class 9 Surface Areas and Volumes

Last updated at April 16, 2024 by Teachoo

Transcript

Example 8
The height and the slant height of a cone are 21 cm and 28 cm respectively. Find the volume of the cone.
Volume of the come = 1/3 𝜋𝑟2ℎ
Given
slant height = l = 28 cm
Height of cone = h = 21 cm
Let radius of cone = r cm
We know that
l2 = h2 + r2
282 = 212 + r2
282 – 212 = r2
r2 = 282 – 212
r2 = (28 – 21) (28 + 21)
r2 = (7) (49)
r = √("7(49)" )
r = √("7(7)2" )
r = 7√7cm
So,
Volume of the come = 1/3 𝜋𝑟2ℎ
= 1/3 × 22/7 × 7 √7 × 7 √7 × 21 cm3
= 22 × 7√7 × 7 √7 cm3
= 22 × 7 × 7 ×(√7)2 cm3
= 22 × 7 × 7 × 7 cm3
= 7546 cm3

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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