A cast iron pipe has 300 mm bore and 10 mm metal thickness, and is supported at two points 8 m apart. What is the internal area of pipe?
- A0.07069 m²Correct
- B1.57059 m²
- C2.67069 m²
- D3.47059 m²
Solution
Concept
Internal area of a pipe is the area of a circle with diameter equal to the bore.
Formula
Aint = (π/4) × d2
Step-by-step solution
1. Bore (inner diameter) d = 300 mm = 0.3 m. 2. Aint = (π/4) × d2 = (π/4) × 0.32. 3. Aint = 0.7854 × 0.09 = 0.07069 m².
Explanation
Bore means the inside diameter of the pipe. So the internal area uses d = 0.3 m. The metal thickness and the 8 m span are not needed for this part.
Why the other options are wrong
B, C and D are much larger than the area of a 0.3 m circle, so they are wrong.
Shortcut
Area of 300 mm circle = 0.7854 × 0.09 ≈ 0.0707 m².
Common mistake
Using the outer diameter (0.32 m) or using radius in place of diameter.
Correct answer: A) 0.07069 m²