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:

Answer: Option B

Explanation:

External radius = 4 cm,

Internal radius = 3 cm.

Volume of iron

=		22	x [(4)² - (3)²] x 21	cm³
		7

=		22	x 7 x 1 x 21	cm³
		7

= 462 cm³.

Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.