How much metal is required to make a 20 metre long pipe, if its inner and…
2026
How much metal is required to make a 20 metre long pipe, if its inner and outer diameter are 6 metre and 8 metre respectively.
- A.
200 m^3
- B.
740 m^3
- C.
300 m^3
- D.
440 m^3
Attempted by 204 students.
Show answer & explanation
Correct answer: D
Key idea: The pipe is a hollow cylinder. Metal required = outer cylinder volume − inner cylinder volume = π(R² − r²) × height.
Find radii: outer radius R = 8/2 = 4 m; inner radius r = 6/2 = 3 m.
Compute R² − r²: 4² − 3² = 16 − 9 = 7.
Compute volume: π × 7 × 20 = 140π.
Evaluate with π = 22/7: 140π = 140 × 22/7 = 20 × 22 = 440.
Answer: 440 m^3