3 One end of a light elastic string of natural length 1.6 m and modulus of elasticity 28 N is attached to a fixed point \(O\). The other end of the string is attached to a particle \(P\) of mass 0.35 kg which hangs in equilibrium vertically below \(O\). The particle \(P\) is projected vertically upwards from the equilibrium position with speed \(1.8 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). Calculate the speed of \(P\) at the instant the string first becomes slack.