4. A light elastic string has natural length 0.4 m and modulus of elasticity 49 N . A particle \(P\) of mass 0.3 kg is attached to one end of the string. The other end of the string is attached to a fixed point \(A\) on a ceiling. The particle is released from rest at \(A\) and falls vertically. The particle first comes to instantaneous rest at the point \(B\).

1. Find the distance \(A B\). The particle is now held at the point 0.6 m vertically below \(A\) and released from rest.
2. Find the speed of \(P\) immediately before it hits the ceiling.