Question

An iron pipe is 21cm long and its external diameter is 8cm. if the thickness of the pipe is 1cm and iron weights 8g/cm³ , find the weight of the pipe.

Answer 1

External diameter of pipe = 8 cm
So, its external radius; R = 8/2 = 4 cm
Thickness of pipe = 1 cm
This means internal radius of pipe; r = external radius - thickness of pipe = 4 - 1 = 3 cm
Length of pipe; h = 21 cm
Now this pipe is in the form of cylinder.
So the volume of pipe = $\mathrm{\pi }\left({\mathrm{R}}^2-{\mathrm{r}}^2\right)\mathrm{h}=\frac{22}{7}\left(4^2-3^2\right)\times 21=\frac{22}{7}\times 7\times 21=462{\mathrm{cm}}^3$
Since weight of 1 ${\mathrm{cm}}^3$ of iron = 8g
So, weight of 462 ${\mathrm{cm}}^3$ of iron = 8 $\times$ 462 = 3696g