Question

How many cubic metres of earth must be dug out
to make a well 20 metres deep and 2 metres in
diameter? Take π to be 22/7
If the inner curved surface of the well in part (1)
above is to be plastered at the rate of ₹5 per m²
find the cost of plastering. Take π to be 22/7.​

Answer 1

Answer:

20 meters deep.. 2meter diameter

Answer 2

Answer :

• ➟ Volume of earth dug out = 440/7 m³.
• ➟ Cost of plastering = ₹880/7 × 5 = ₹4400/7 = ₹628.57.

Step-by-step Explanation :

Given that :

• ➟ Depth of well (h) = 20 m.
• ➟ Diameter (d) = 2 m.
• ➟ The inner curved surface of the well in part (1) above is to be plastered.
• ➟ Cost of plastering per m² = ₹5.

To find :

• ➟ Cost of plastering the inner curved surface of the well in part (1).

Formulae Used :

• ➟ Radius (r) = d/2.
• ➟ Volume of earth dug out = πr²h.
• ➟ Inner curved surface area = 2πrh.

Radius :

• ➟ Radius (r) = d/2.
• ➟ R = 2/2.
• ➟ R = 1.

Volume of earth dug out :

• ➟ Volume of earth dug out = πr²h.
• ➟ Volume of earth dug out = (22/7) × 1² × 20.
• ➟ Volume of earth dug out = 440/7 m³.

Inner curved surface area :

• ➟ Inner curved surface area = 2πrh.
• ➟ Inner curved surface area = 2 × 22/7 × 1 × 20 = 880/7 m².

Cost of plastering :

• ➟ Cost of plastering = ₹880/7 × 5 = ₹4400/7 = ₹628.57.