1. The problem statement, all variables and given/known data A system consists of two blocks, of masses m and 2m, attached to the ends of a massless spring with a force constant k. The system is placed on a horizontal frictionless surface. Initially, the spring is relaxed. The blocks are then pulled apart an “extra” distance x and simultaneously released from the state of rest. Find the speed v1 of the block of mass m at the instant the spring is relaxed again. Answer in terms of m, k, and x. 2. Relevant equations U_spring = 1/2*k*x^2 K = 1/2*m*v^2 m_1*v_1+m_2*v_2 = m_1*v_1' + m_2*v_2' 3. The attempt at a solution Momentum is conserved and initially 0 so m*v_1 = 2m*v_2 and v_1 = 2v_2 Potential energy in the compressed spring is equal to 1/2*k*x^2 and when the spring reaches equilibrium the potential is 0 and the kinetic energy is equal to 1/2*m*v_1^2+1/2*(2m)*(2v_1)^2 so 1/2*k*x^2 = 1/2*m*v_1^2+4*m*v_1^2 = k*x^2 = m*v_1^2+8*m*v_1^2 = k*x^2 = 9*m*v_1^2 and finally v_1 = sqrt(k*x^2/(9*m)) Where am I going wrong?