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/cm${}^3$, then the weight of the pipe is:

• A. 3.6 kg
• B. 3.696 kg
• C. 36 kg
• D. 36.9 kg
• E. 369 kg

Answer 1

The correct option is B

3.696 kg

Volume of iron = $\frac{22}{7}\times [(4{)}^2-(3{)}^2]\times 21$ cm${}^3$ = $\left(\frac{22}{7}\times 7\times 21\right)$cm${}^3$ = 462 cm${}^3$ $\therefore$Weight of Iron = (462 $\times$ 8) gm = 3696 gm = 3.696 kg