Question

I NEED HELP PLEASE. Calculate the inner area of a pipe with an outer diameter of 300mm and a thickness of 5mm. What length of pipe can be manufactured from `10^6 cm^3`?

Answer 1

`=215.8m`

Explanation:

Think of the pipe being composed of `3` parts.

• the entire pipe - diameter of `300mm` radius = `150mm`
• the inner part - diameter of `290mm` radius = 145mm#
• the metal part which makes the pipe.

The length is not given, but the volume is.

Find the area of metal in the cross-section - called a washer.

Area = area of Big circle- area of inner circle

The inner area = `pi xx 145^2 = 21,025 pi" " mm^2`

`A = piR^2 - pir^2`

`A = pi(R^2-r^2)`

`A = pi(R+r)(R-r)`

`A = pi(150+145)(150-145)`

`A = pi xx295 xx 5`

`A=4633.85 mm^2`

`A = 4633.85 div 100 = 46.338 cm^2`

`V = " area of cross-section" xx "length"`

`"length" = V/A = 10^6/46.338 cm`

`=21,580.33cm`

`=215.8m`