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

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?

Right Option : C
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Explanation
Question : 2

The slant height and base diameter of a conical tomb are 25 m and 14 m respectively. Find the cost of white-washing its curved surface at the rate of Rs 210 per 100 m^{2}.

Right Option : A
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Explanation
Question : 3

The area of the curved surface of a cone is 60pi cm^{2}. If the slant height of the cone be 8 cm, find the radius of the base.

Right Option : B
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Explanation
 
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