A copper wire of length 3 m and area of cross-section `1mm^(2)` passes through an arrangement of two friction-less pulleys `P_(1)` and `P_(2)`. One end of the wire is rigidly clamped and a mass of 1 kg is hanged from the other end if the young's modulus for copper is `10xx10^(10)N//m^(2)` , then the elongation in the wire is