A copper wire, 3 mm in diameter, is wound about a cylinder whose length is 12 cm, and diameter 10 cm, so as to cover the curved surface of the cylinder. Find the length and mass of the wire, assuming the density of copper to be 8.88 g per cm3.

It can be observed that 1 round of wire will cover 3 mm height of cylinder.
Therefore, the number of round = Height of cylinder/Diameter of wire = 12/0.3 = 40
Lenght of wire for one round = radius of cylinder
= 2πr = 2π × 5 = 10π
Length of wire to wound 40 times = 40 × 10π
= (400 × 22/7) = 8800/7
= 1257.14 cm = 12.57 m
Radius of wire = 0.15 cm
Volume of wire = Area of cross- section of wire × length
= π(0.15)² × 1257.14 = 88.898 cm³
Mass = Volume × Density = 88.898 × 8.88 = 789.41 gm