If the round steel with a diameter of 40mm and a length of 1m is straightened into a steel wire with a diameter of 40mm, the length of the steel wire is (solving the equation, it is best to have steps! ) Thinking of solving problems: constant volume

Original Volume = Straightened Volume

Volume = cross-sectional area * length

The cross-sectional area is circular, and the radius is deduced from the known diameter and calculated by the formula of circular area.

Pay attention to the unit in the process of solving. It is best to unify the units before formulating the formula.