Question

Find the total surface area of an open pipe of length 50 cm, external diameter 20 cm and internal diameter 6 cm.

Answer 1

Length of an open pipe = 50 cm 

External diameter = 20 cm `=>` External radius (R) = 10 cm 

Internal diameter = 6 cm `=>` Internal radius (r) = 3 cm 

Surface area of pipe open from both sides = 2πRh + 2πrh

= 2πh(R + r)

= `2 xx 22/7 xx 50 xx (10 + 3)`

= 4085.71 cm²

Area of upper and lower part = 2π(R² – r²)

= `2 xx 22/7 xx (10^2 - 3^2)`

= `2 xx 22/7 xx (100 - 9)`

= `2 xx 22/7 xx 91` 

= 572 cm²

Total surface area = 4085.714 + 572

= 4657.71 cm²