1. The problem statement, all variables and given/known data A block of mass m is suspended through a spring of spring constant k[I/] and is in equilibrium. A sharp blow gives the block an initial downward velocity v. How far below the equilibrum position does the block come to an instantaneous rest? 2. Relevant equations Potential energy of a compressed or extended spring: 1/2 kx2 Gravitational Potential energy: mgh 3. The attempt at a solution When the block is at equilibrium, kx = mg. This implies x = mg/k Potential energy of the spring in this position = 1/2 kx2 = (mg)2/2k Taking the gravitational potential energy to be zero in this position, total mechanical energy = 1/2 mv2 + (mg)2/2k. I can't figure out where to go from there.