A metal pipe has a bore (inner diameter) of 5 cm. The pipe is 5 mm thick all round. Find the weight, in kilogram, of 2 metres of the pipe if 1 cm³ of the metal weights 7.7 g.

Given,

Inner diameter = 5 cm and thickness of pipe = 5 mm = 0.5 cm.

Inner radius of the pipe (r) = $\dfrac{5}{2}$ = 2.5 cm.

External radius of the pipe (R) = Inner radius of the pipe + Thickness of the pipe

= 2.5 cm + 0.5 cm = 3 cm

Length of the pipe (h) = 2 m = 200 cm.

Volume of the pipe = External Volume - Internal Volume

= πR²h - πr²h

= π(R² - r²)h

= π(R + r)(R - r) h

= $\dfrac{22}{7}$(3 + 2.5)(3 - 2.5) x 200

= $\dfrac{22}{7} \times$(5.5) x (0.5) x 200 = 1728.6 cm³.

Given, 1 cm³ of the metal weight 7.7 g,

∴ Weight of the pipe = (1728.6 x 7.7) g = $\dfrac{(1728.6 \times 7.7)}{1000}$ kg = 13.31 kg.

Hence, weight of the pipe = 13.31 kg.