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 $(\frac{22}{7}\times [(4{)}^2-(3{)}^2\times 21\left)c{m}^3\right)$
$=(\frac{22}{7}\times 7\times 1\times 21c{m}^3)$
$\therefore$ weight of iron=$(462\times 8)$ gm =3696 gm=3.696 kg.