Lateral Surface Area of Cone

Concept Explanation

Lateral Surface Area of Cone

Lateral Surface Area of Cone: The curved surface area of a cone is also called the lateral surface area. Lateral surface area of cone $=pi rl$

where r = radius of the base of the cone and l = slant height of the cone and $large l=sqrt{r^2+h^2}$

Illustration: The circumference of the base of a 10m height conical tent is 44m. Calculate the length of canvas used in making the tent if width of canvas is 2m.

Solution: Given: Circumference of cone = 44 m and h =10m and breadth = 2 m

So, we have, $large 2pi r$ = 44m ..............(i)

So, Using equation (i), we have

$large 2times frac{22}{7}times r=44$

$frac{44}{7}times r=44$

$r=44times frac{7}{44}$

$r=7;m$

As we know Area of Canvas = Curved Surface Area of Cone

Area of Canvas = length x breadth = length x 2 ...................(ii) [As breadth = 2 m]

$large therefore; l=sqrt{r^2+h^2}=sqrt{49+100}=sqrt{149}m$ = 12.2 m

$large Lateral ;surface;area=pi rl=frac{22}{7}times 7times sqrt{149}m^2=268.4m^2$

Now, using equation (ii), we have

Area of Canvas = length x 2

length $=frac{area ;of; canvas}{2}$

Length of canvas = $large frac{268.4}{2}=134.2m$

Illustration: The radius and slant height of a cone are in the ratio 4 : 7. If its curved surface area is 792 sq cm, find its radius. (Use $large pi =frac{22}{7}$ )

Solution: Let r cm be the radius and l cm the slant height of the cone. Then,

r : l = 4 : 7

Let the common factor = x

$large therefore r= 4x$ cm and $large l= 7x$ cm ........................(i)

Now, curved surface area = 792 sq cm

$large pi rl =792$

$large frac{22}{7}times 4xtimes 7x=792$

$large x^{2}=frac{792}{88}$

$large x^{2}=9$

$large x=pm 3$

But x = - 3 is not possible.

Hence, x = 3

Using x = 3 in equation (i), we have

$large r= 4x=4(3)$

$large r=12$ cm

Hence radius of the base of the cone is 12 cm.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

The radius of a cone is 7 cm and area of curved surface is 176 sq cm. Find the slant height.
A. 6 cm	B. 7 cm	C. 8 cm	D. 5 cm
Right Option : C
View Explanation

Question : 2

The area of the curved surface of a cone is 60 $pi$ $cm^{2}$ . If the slant height of the cone be 8 cm, find the radius of the base.
A. 7.5	B. 6.5	C. 7.3	D. 7.2
Right Option : B
View Explanation

Question : 3

A corn cob, shaped somewhat like a cone, has the radius of its broadest end as 2.1 cm and length as 20 cm. If each 1 $cm^{2}$ of the surface of the bob carries an average of four grains, find how many grains you would find on the entire cob?
A. 530	B. 529	C. 531	D. 532
Right Option : C
View Explanation

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