A sector of radius 10.5cm with the central angle 120° is folded to form a cone by joining the two bounding radii of the sector. What is the volume (in cm3) of the cone so formed?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 
When the sector of the circle is folded to form a cone,
the slant height of the cone = radius of the cone = 10.5 cm
Perimeter of the sector of the circle = length of base of cone
2π r x angle/360 = 2πr [R = 10.5/3 = 3.5]
Height of cone = h
By Pythogorous Theorem
h2 = (10.5)2 - (3.5)2
h2 = 110.25 - 12.25
h = √98
Volume of cone = 1/3 x πr²h
= 1/3 x π x (3.5)² x √98