A particle, P, of mass 3.5 kg is attached to one end of a light, elastic string, of natural length 1.2 m. The other end of the string is attached to a fixed point, 0. The particle is allowed to rest in equilibrium with P 1.8m below 0.

a. Show that the modulus of elasticity λ is 7gN.

b. The particle is now pulled horizontally to the side by a force of magnitude XN so that the angle between the string and the downward vertical is 60°. Given that the particle is at the same vertical level as it was before, find the value of X.