A spring has an unstretched length of 0.650 and a weight of 0.400kg is attached and gently lowered till eqm point is reached. The spring is then stretched by a distance of 0.200m. Loss in gpe=mgh=0.200x0.650x9.81=0.785 J Gain in EPE=0.5 Fx= 0.5 x 0.400x 9.81 x 0.200=0.392 (???) Actually I dont really understand why this is so. But it is the answer. Why are the two answers different? Furthermore, if the spring is set into SHM with amplitude 0.200m, what is the resultant force at the lowest point of movement?