Question

A hollow iron pipe of $21cm$ long and its external diameter is $8cm$. If the thickness of the pipes is $1cm$ and iron weights $8g/c{m}^2$, then the weight of the pipe is equal to

• A. $3.6kg$
• B. $3.696kg$
• C. $36kg$
• D. $36.9kg$

Answer 1

The correct option is B $3.696kg$

Volume of a hollow Cylinder of outer Radius "R", inner Radius ""r" and height "h"

$=\pi (R^2-r^2)h$

Outer Radius $=\frac{8}{2}=4cm$

Inner Radius $=4-1=3cm$

Hence, volume of the pipe $=\frac{22}{7}\times (4^2-3^2)\times 21=462{cm}^3$

Weight of the pipe $=462\times 8g=3696g=3.696kg$