55. An iron pipe 20 cm long has exterior diameter25 crn. If the thickn

1.	55. An iron pipe 20 cm long has exterior diameter25 crn. If the thickness of the pipe is 1 cm, findthe "whole surface area of the pipe. IT-11 {2011]
Answer» External diameter of the iron pipe=25 cm =>external radius=rₑ=25/2 cmThickness=t=1 cm=>Internal radius=rᵢ=25/2-1=23/2 cm.Length of the iron pipe=h=20 cm ∴Total surface area=2πrₑh+2πrᵢh+2{π(rₑ²-rᵢ²)}=2×3.14×25/2 ×20 + 2×3.14×23/2×20+ 2{π((25/2)²-(23/2)²)} =3165.12 cm²

55. An iron pipe 20 cm long has exterior diameter25 crn. If the thickness of the pipe is 1 cm, findthe "whole surface area of the pipe. IT-11 {2011]

Answer»

External diameter of the iron pipe=25 cm

=>external radius=rₑ=25/2 cmThickness=t=1 cm=>Internal radius=rᵢ=25/2-1=23/2 cm.Length of the iron pipe=h=20 cm

∴Total surface area=2πrₑh+2πrᵢh+2{π(rₑ²-rᵢ²)}=2×3.14×25/2 ×20 + 2×3.14×23/2×20+ 2{π((25/2)²-(23/2)²)} =3165.12 cm²