A thick cylindrical pipe of length 1.4 m open at both the ends has internal and external diameters 60 cm and 80 cm, respectively. It is to be painted from all sides. What will be the cost of painting (in ₹) if the rate of painting is ₹110 / m2? (Use π = 22/7)
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 726.
Total surface area to be painted = CSA(internal) + CSA(external) + Area of both edge rings
Internal radius of cylinder, r1 = 30 cm = 0.3 m
External radius of cylinder, r2 = 40 cm = 0.4 m
Now CSA of cylinder =
CSA (internal) = 2 × (22/7) × 0.3 × 1.4
⇒ 44 × 0.06 = 2.64
CSA (external) = 2 × (22/7) × 0.4 × 1.4
⇒ 44 × 0.08 = 3.52
Area of both ring edges = 2π(r22 - r12)
⇒ 2 × (22/7) × (0.16 - 0.09)
⇒ 2 × (22/7) × 0.07 = 0.44
Total surface area to be painted = 2.64 + 3.52 + 0.44 = 6.60 m2
Total cost of painting = 6.60 × 110 = 726