4 One end of a light elastic string, of natural length 0.75 m and modulus of elasticity 44.1 N , is attached to a fixed point \(O\). A particle \(P\) of mass 1.8 kg is attached to the other end of the string. \(P\) is released from rest at \(O\) and falls vertically. Assuming there is no air resistance, find

1. the extension of the string when \(P\) is at its lowest position,
2. the acceleration of \(P\) at its lowest position.