CBSE Class 9 Answered

the length of the arc of the sector will become the circumference of the base of the cone.

Let the radius of the base of the cone =R.

So using the length of arc formula for the sector of radius 12 and angle 120 degrees, we get

(120/180)(22/7)(12)=2*(22/7)R

so,

R=4

This is the base radius of the cone and the radius of the sector becomes the slant height of the cone.

so straight height of the cone =

h=sqrt of(144-16)=sqrt(128)

use these values of R and h to get the volume.