Question

how many cubic meters of earth must be dug out to make a well 28 m deep and 2.8 m in diameter?also find the cost of plastering its inner surface at ₹4.50 per sq metre

Answer 1

h=28m;
r=1.4m;

earth dug out=volume of cylinder=22/7*r*r*h;
= 22/7*1.4*1.4*28;
=172.48 m^3
hence 172.48m^3 of earth is dug out

The curved surface area of cylinder
=2*22/7*1.4*28;
=246.4
Cost of plastering=4.50*246.4
=Rs 1108.8

Answer 2

Find the radius:

Radius = Diameter ÷ 2

Radius = 2.8 ÷ 2 = 1.4 m

Find the volume:

Volume = πr²h

Volume = π (1.4)²(28)

Volume = 172.48 m²

Find the inner surface area:

Surface area = πr² + 2πrh

Surface area = π(1.4)² + 2π(1.4)(2.8)

Surface area = 6.16 + 24.64

Surface area = 30.8 m²

Find the cost of plastering:

1 m² = ₹4.50

30.8 m² = 4.5 x 30.8 = ₹ 138.60

Answer: 172.48 m² of earth needs to be dug out and the cost of plastering is ₹ 138.60