Question

A hollow cylindrical tube open at both ends is made of iron $2cm$ thick. If the external diameter be $50cm$ and the length of the tube is $140cm$, find the number of cubic cm of iron in it.

Answer 1

Volume of cylinder $=\pi .r^{2}h$

Height of cylinder $=140cm$

External diameter $=50cm$

$\therefore$ External radius $=25cm$ $=OB$

Internal radius $=OB-AB$

$=25-2=23cm$

Volume of iron $=$ Vol. of cylinder of radius $25cm$-Vol. of cylinder of radius $23cm$.

$=\frac{22}{7}\times 25\times 25\times 140-\frac{22}{7}\times 23\times 23\times 140$

$=42240$ cubic cm