2 A particle of mass 0.2 kg is attached to one end of a light elastic string of natural length 0.6 m and modulus of elasticity 4 N . The other end of the string is attached to a fixed point \(O\). The particle is held at a point which is \(( 0.6 + x ) \mathrm { m }\) vertically below \(O\). The particle is released from rest. In the subsequent motion the speed of the particle is \(3 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) when the string becomes slack. By considering energy, find the value of \(x\).