Question 60

A sector of a circle of radius 21 cm and central angle $$120^\circ$$ is folded into a cone. Radius of the cone thus obtained is:

Solution

Circumference of Circle = $$2\pi r=2\times\frac{22}{7}\times21=132\ cm.$$

So, Circumference of the sector is = $$\left(\frac{120}{360}\times132\right)\ cm=44\ cm.$$

This is the circumference of base of the Cone extracted .

So, $$2\times\frac{22}{7}\times r_{cone}=44\ .$$

or, $$r_{cone}=7 cm.$$

A is correct choice.

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