A 120° sector of a circle of radius 21cm is bent to form a cone. What is the base radius of the cone?
- A.
3^{1}/_{2}cm - B.
7cm - C.
1O^{1}/_{2}cm - D.
14cm - E.
21cm
Correct Answer: Option B
Explanation
The length of the arc subtended by the sector of angle 120° = circumference of the base of the cone.
(frac{120}{360} times 2 times frac{22}{7} times 21 = 2pi r)
(44 = 2pi r)
(r = 22 div pi)
(r = 22 times frac{7}{22})
r = 7 cm