The diameter of the lower and upper ends of a bucket in the form of a frustum of a cone are 10 cm and 30 cm respectively. If its height is 24 cm. find:
(i) The capacity of the bucket
(ii) The area of the metal sheet used to make the bucket. [Take π = 3.14.]
Given,
Radius of lower end, r2 = 10 cm
Radius of upper end, r1 = 30 cm
Height of bucket, h = 24 cm
(i) As we know
volume of frustum of a cone =
Where, h = height, r1 and r2 are radii of two ends (r1 > r2)
Capacity of bucket =
=3.14 × 8 × (100 + 900 + 300)
= 3.14 × 8 × 1300 = 32656 cm3
(ii) Area of metal used to make bucket = CSA of frustum + base area
We know that,
Curved surface area of frustum = πl(r1 + r2)
Where, r1 and r2 are the radii of two ends (r1 > r2)
And l = slant height and
l = √(h2+ (r1 – r2 )2)
So, we have
Slant height, l=√(242 + (30 – 10)2)
⇒ l =√(576 + 100)
⇒ l =√676
⇒ l =26 cm
And as the base has lower end,
Base area = πr22, where r2 is the radius of lower end
Therefore,
Area of metal sheet used = πl(r1 + r2) + πr22
= π(26)[10 + 30] + π(10)2
= 1040π + 100π = 1140π
= 1140(3.14) = 3579.6 cm2