Question

"Question 2 It is required to make a closed cylindrical tank of height 1 m and base diameter 140 cm from a metal sheet. How many square meters of the sheet are required for the same?

Class 9 - Math - Surface Areas and Volumes Page 216"

Answer 1

Let r be the radius of the base and h be the height of the cylinder.

Base diameter = 140 cm and Height (h) = 1m

Radius of base (r) = 140/2 = 70 cm = 0.7 m

Metal sheet required to make a closed cylindrical tank = 2πr(h + r)
= (2 × 22/7 × 0.7) (1 + 0.7) m2
=7.48 m2

Answer 2

total area of tank = surface area of cylinder + 2 × cross section area of tank
= 2πrL + 2πr²
= 2πr ( L + r)

Given,
diametre of base = 140 cm
radius of base (r) = 70cm
height of tank (L) = 1 m = 100 cm

total area = 2πr(L + r)
= 2 × 22/7 × 70 × ( 100 + 70)
= 20 × 22 × 170 cm²
= 74800 cm²
= 7.48 m²

hence, 7.48 m² sheets are required for the making tank