area of right circular cylinder

Question

320 numbers of steel pipes, each of outer diameter 1.4m were used in laying a pipe-line from an oil collecting station to an oil Refinery. If the area of the outer curved surface of a pipe is 66m². Find the length of the whole pipe-line.

Answer 1

The area of the curved surface is the area of a rectangle (just take a piece of paper, hold the outer edges of the sheet to each other to make a cylinder and it will make sense), where one side is the length of the pipe and the other - circumference of the pipe. So, if your area is 66 m², to find the length of the pipe, divide it by 2PiR or, in your case by d*Pi (since R = d/2). So, we'll get 66/(1.4Pi) for the length of each pipe. And since there are 320 of those pipes, your answer is 320*66/(1.4Pi)