1. The problem statement, all variables and given/known data A plunger of mass m rests on a spring with constant k. The spring is pressed down a distance x and released from rest. How large does the the mass need to be in order to keep the plunger in contact with the spring? 2. Relevant equations PEf+KEf=PEi kx-mg+N=0 3. The attempt at a solution Using the Conservation of energy equation and solving for m, I get: kx2/(2gh+vf2) = m I have a suspicion that I somehow have to incorporate the second equation into the answer, but am stumped as to how I proceed.