5 A particle \(P\) of mass 0.7 kg is attached by a light elastic string to a fixed point \(O\) on a smooth plane inclined at an angle of \(30 ^ { \circ }\) to the horizontal. The natural length of the string is 0.5 m and the modulus of elasticity is 20 N . The particle \(P\) is projected up the line of greatest slope through \(O\) from a point \(A\) below the level of \(O\). The initial kinetic energy of \(P\) is 1.8 J and the initial elastic potential energy in the string is also 1.8 J .
- Find the distance \(O A\).
.................................................................................................................................... - Find the greatest speed of \(P\) in the motion.