A rectangular piece of copper foil of length 21 cm and area 1386 cm2 is folded along its width to form a cylinder such that there is only one layer of copper foil on any part of the cylinder. What is the volume (in cm3) of the cylinder so formed?

Solution

Width of the rectangular piece of copper foil = 1386/21 = 66 cm Since the foil is folded along its width to form a cylinder without any double layer, circumference of the cylinder formed = width of the rectangular foil Also, height of the cylinder so formed = length of the rectangular copper foil So, 2 × π × radius = 66 Radius of cylinder = 66 ÷ (2 × 22/7) = (66/44) × 7 = 10.5 cm So, volume of the cylinder so formed = π × (radius)² × height = (22/7) × 10.5 × 10.5 × 21 = 7276.5 cm³