A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the…
2024
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
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Correct answer: B
Given: hollow iron pipe with length 21 cm, external diameter 8 cm, thickness 1 cm, and iron density 8 g/cm^3.
Find radii: external radius R = 8/2 = 4 cm; internal radius r = R − thickness = 4 − 1 = 3 cm.
Volume of iron (hollow cylinder) = π(R² − r²)h = (22/7) × (4² − 3²) × 21.
Compute: (22/7) × (16 − 9) × 21 = (22/7) × 7 × 21 = 22 × 21 = 462 cm³.
Weight = volume × density = 462 cm³ × 8 g/cm³ = 3696 g = 3.696 kg.
Answer: 3.696 kg