1. The problem statement, all variables and given/known data A light elastic string has a natural length 1 m. One end of the string is attached to the fixed point O and a particle P of mass 4 kg is suspended from the other end of the string. When hanging in equilibrium, P is 1.2 m below O. #1 Find the modulus of elasticity of the string. When P is hanging in equilibrium, it is hit from below by a particle Q, of mass 2 kg, which is travelling vertically upwards. Immediately after the impact, P moves vertically upwards with a velocity u m/s. When the string is just taut, P is still moving vertically upwards with a velocity of √10 m/s. #2 Find the value of u. Given that Q is moving with a velocity of 4√3 m/s upwards before it hits P, #3 show that it is momentarily at rest just after impact. #4 Find the position of the lowest point, with respect to the equilibrium point, reached by P in the subsequent motion. 2. Relevant equations Young's modulus of elasticity (λ) λ = (F/A)/(ΔL/Lo) F - force A - cross sectional area ΔL - change in length Lo - original length g = 10 m/s^2 I'm also guessing you're gonna be using the formulas for Conservation of Energy, Ki + Pi = Kf + Pf, right? I'm not so sure what other equations can be used 3. The attempt at a solution So the cross sectional area, A, was not given in the problem. I just assigned a variable A for it so my λ = [(4 kg)(10 m/s^2)/A] / [(0.2)/(1)] = 200A Sadly this is what I can do for now. Still thinking about the rest. Can anyone help?