Question

The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find

(i) Its inner curved surface area,

(ii) The cost of plastering this curved surface at the rate of Rs 40 per m².

[ Assume π = 22/7 ]

Answer 1

Inner radius (r) of circular well = (3.5/2)m = 1.75m

Depth (h) of circular well = 10 m

Inner curved surface area = 2πrh

= (2 x 22/7 x 1.75 x 10) m²

= (44 x 0.25 x 10) m²

= 110 m²

Therefore, the inner curved surface area of the circular well is 110 m².

Cost of plastering 1 m² area = Rs 40

Cost of plastering 100 m² area = Rs (110 × 40) = Rs 4400

Therefore, the cost of plastering the CSA of this well is Rs 4400.