Mathematics

A 120° sector of a circle of radius 21cm is bent to form a cone….

A 120° sector of a circle of radius 21cm is bent to form a cone. What is the base radius of the cone?

  • A.
    31/2cm
  • B.
    7cm
  • C.
    1O1/2cm
  • 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