2. A light elastic string \(A B\) has one end \(A\) attached to a fixed point on a ceiling. A particle \(P\) of mass 0.3 kg is attached to \(B\). When \(P\) hangs in equilibrium with \(A B\) vertical, \(A B = 100 \mathrm {~cm}\). The particle \(P\) is replaced by another particle \(Q\) of mass 0.5 kg . When \(Q\) hangs in equilibrium with \(A B\) vertical, \(A B = 110 \mathrm {~cm}\). Find
- the natural length of the string,
- the modulus of elasticity of the string.