Total Surface Area of Frustum


 
 
Concept Explanation
 

Total Surface Area of Frustum

Total Surface Area of Frustum: If a cone is cut by a plane parallel to the base of the cone, then the portion betweenthe plane and base is called the frustum of the cone. Let "h" be the height, "l" the slant height and large r_{1} and large r_{2} the radii of the ends large (r_{1}>r_{2}) of the frustum of a cone.Then we can directly find the total surface are of frustum by using the formulae given below : Total surface area of the frustum of the cone large =pi l(r_{1}+r_{2})+pi r^{2}_{1}+pi r^{2}_{2}   OR it can be expressed as Total surface area of bucket large =pi left [ (r_{1}+r_{2})l+r_{2} right ]

Example: If the radii of the ends of the frustum of 24 cm high cone are 5 cm and 15 cm, find the total surface area of the bucket.

Solution: If R and r be the radii and h the height and l the slant height of the frustum of the cone, thenlarge l=sqrt{h^{2}+(R^{2}-r)^{2}}large =sqrt{(24)^{2}+(15-5)^{2}}=sqrt{676}. Hence l = 26cm

Total surface area large =pi [R^{2}+r^{2}+l(R+r)]large =frac{22}{7}[225+25+26(15+5)]large =frac{22}{7}times[250+520]=frac{22}{7}times770=2420cm^{2}

Sample Questions
(More Questions for each concept available in Login)
Question : 1

An oil funnel made of tin sheet consists of a 10 cm long cylindrical portion attached to a frustum of a cone. If the total height is 22 cm, diameter of the cylinderical portion is 8 cm and the diameter of the top of the funnel is 18 cm, find the area of the tin sheet required to make the funnel.

Right Option : D
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Question : 2

A container, opened from the top and made up of a metal sheet, is in the form of a frustum of a cone of height 16 cm with radii of its lower and upper ends as 8 cm and 20 cm respectively. Find the cost of the milk which can completely fill the container, if it costslarge Rs8;per;100cm^2.large (Take;pi=3.14)

Right Option : A
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Question : 3

The slant height of a frustum of a cone is 4 cm and the perimeters of its circular ends are 18cm and 6cm. Find the curved surface area of the frustum.

Right Option : C
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Explanation
 
 
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