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… · ABC26GN4935

Subject: General Aptitude · Chapter: Volume and Surface Area

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 $8 \mathrm{g} / \mathrm{cm}^{3}$, then the weight of the pipe is

(a)3.6 kg

(b)3.696 kg

(c)36 kg

(d)36.9 kg

Answer

Answer (as printed): B

Explanation

External radius $=4 \mathrm{cm}$, Internal radius $=3 \mathrm{cm}$. Volume of iron $$\begin{aligned} =\left\{\frac{22}{7} \times\left[(4)^{2}-(3)^{2}\right] \times 21\right\} \mathrm{cm}^{3} & =\left(\frac{22}{7} \times 7 \times 1 \times 21\right) \mathrm{cm}^{3} \\ & =462 \mathrm{cm}^{3} . \end{aligned}$$ ∴ Weight of iron $=(462 \times 8) \mathrm{gm}=3696 \mathrm{gm}=3.696 \mathrm{kg}$.

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