3 One end of a light elastic string of natural length 0.4 m and modulus of elasticity 20 N is attached to a fixed point \(O\). The other end of the string is attached to a particle \(P\) of mass \(0.25 \mathrm {~kg} . P\) hangs in equilibrium below \(O\).

1. Calculate the distance \(O P\). The particle \(P\) is raised, and is released from rest at \(O\).
2. Calculate the speed of \(P\) when it passes through the equilibrium position.
3. Calculate the greatest value of the distance \(O P\) in the subsequent motion.