Question

from a circle of 15 cm, a sector with angle 216 radius is cut out and it's bounding radii are bent so as to form a cone. find its volume.



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Answer 1

v = πr²h/3 .

The sectoral arc becomes the perimeter of the base circle. 

2πr = (216/360)[2πR] 

=> r/R = 216/360 

r = 15 X (216/360) 

= 216/24 = 9 cm. 

And h² = s² - r² . . . {Pythagoras theorem} 

= 15² - 9² = 3²(5² - 3²) = 3²(4²) = 12² 

h = 12 . 

substitute the values and you can find the volume