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:
Answer: Option B
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External radius = 4 cm,
Internal radius = 3 cm.
Volume of iron = \(\left(\frac{22}{7}\times\left[(4)^{2}-(3)^{2}\right]\times21
\right)cm^{3}\)
= \(\left(\frac{22}{7}\times7\times1\times21\right)cm^{3}\)
= 462 cm3.
So, Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.
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