Question

A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm³, then the weight of the pipe is

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

Answer 1

The correct option is B

3.696 kg

External radius= 4 cm,
Internal radius = 3 cm
Volume of iron $=(\frac{22}{7}\times 7\times [(4{)}^2-(3{)}^2]\times 21)$
$=(\frac{22}{7}\times 7\times 1\times 21)$
$=462c{m}^3$
$\therefore$ Weight of iron = (462 $\times$ 8) gm = 3696 g= 3.696 kg