A 2-kg block is attached to a horizonal ideal spring with a spring constant of 200 N/m. When the spring has its equilibrium length the block is given a speed of 5 m/s. What is the maximum elongation of the spring? Is not the solution simply: 1/2kx2 = 1/2mv2 x = (mv2/k)0.5 x = 0.5 m? That is incorrect, though.