Volume of Frustum


 
 
Concept Explanation
 

Volume of Frustum

Volume of Frustum: If a cone is cut by a plane parallel to the base of the cone, then the portion between the 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} are the radii of the ends large (r_{1}>r_{2}) of the frustum of a cone. Then we can directly find the volume, the curved surface area and the total surface area of frustum by using the formulas given: Volume of frustum of cone large =frac{1}{3}pi h(r^{2}_{2}+r_{1}r_{2})

Example : If the radii of the circular ends of a conical bucket which is 45 cm high, are 28 cm and 7 cm. Find the capacity of the bucket ( Use large pi =22/7 ).

Solution: Clearly, bucket forms a frustum of a cone such that the radii of its circular ends are large r_{1}=28cm,r_{2}=7cm  and height h = 45 cm.

Therefore, capacity of the bucket = Volumne of the frustum large =frac{1}{3}pi h(r^{2}_{2}+r^{2}_{2}+r_{1}r_{2})Capacity of the bucket dpi{120} large =frac{1}{3}times frac{22}{7}times 45(28^{2}+7^{2}+28times 7)=22times frac{15}{7}times 7(4^2times 7 +7+28)= 22 x 15 x (16 x 7 +7 + 28) = 330 x 147 large =48510cm^{3}

Sample Questions
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Question : 1

A drinking glass is in the shape of frustum of a cone of height 7cm. The diameters of its two circular ends are 6cm and 4cm. Find the capacity of the glass. (Use pi =frac{22}{7}).

Right Option : B
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Question : 2

A drinking glass is in the shape of frustum of a cone of height 14cm. The diameters of its two circular ends are 4cm and 2cm. Find the capacity of the glass. (Use large pi =frac{22}{7}).

Figure required

Right Option : A
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Explanation
 
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