area of right circular cylinder

Question

A 10m long iron pipe has a thickness of its wall of 3.5cm and its inside diameter is 15.4cm. Find the cost of painting its outside surface at the rate of 140 per m².

 

Urgently required!

Answer 1

Hi Sandy, the surface area of a pipe is equal to the circumference of the pipe times the length of the pipe. Starting with the inner diameter of the pipe equal to 15.4 cm, you have to add 2 times the wall thickness of the pipe, or 3.5 cm, to get the diameter of the outside of the pipe.

 

The outside diameter of the pipe is equal to 15.4 + 2 * 3.5 = 15.4 + 7 = 22.4 cm.

 

The surface area equals 1000 * pi * 22.4 ≈ 70372 cm², note this is rounded to whole numbers.

 

Convert square centimeters to square meters:

 

10000 cm² = 1 m²

 

Divide 70372 / 10000 to get the surface area in square meters.

 

Surface area in square meters equals 7.0372.

 

To get the cost of painting the surface of the pipe, multiply 140 times 7.0372, which equals $985.21.

 

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