A metal pipe is 42 cm long. The inner diameter of its cross-section is 6 cm.…
2026
A metal pipe is 42 cm long. The inner diameter of its cross-section is 6 cm.
The outer diameter is 6.4 cm. Its inner curved surface area is:
Answer: C. 792 cm2 — ConceptThe inner curved surface of a hollow pipe is the lateral surface of its inner cylinder. For a cylinder, curved surface area equals circumference ×…
- A.
892 cm2
- B.
528 cm2
- C.
792 cm2
- D.
968 cm2
Attempted by 10 students.
Show answer & explanation
Correct answer: C
Concept
The inner curved surface of a hollow pipe is the lateral surface of its inner cylinder.
For a cylinder, curved surface area equals circumference × length: CSA = πdh = 2πrh. Therefore, the inner diameter is used; the outer diameter would describe the outer curved surface.
Application
Inner diameter d = 6 cm, length h = 42 cm, and π = 22/7.
Inner curved surface area = πdh.
CSA = (22/7) × 6 × 42.
Since 42 ÷ 7 = 6, CSA = 22 × 6 × 6.
CSA = 792 cm2.
Cross-check
Using the inner radius r = 3 cm gives 2πrh = 2 × (22/7) × 3 × 42 = 792 cm2, which agrees with the diameter-based calculation.
Therefore, the inner curved surface area is 792 cm2.