The block B has a weight of 10 kg, whereas block A has a weight of 5 kg. When B is released from rest it travels down. Calculate the speed when it has travelled 3 m down. Calculate the displacement of the spring k = 500 N/m to bring the block B to a momentary halt.
  Two seperate datums are required to be established at initial displacements of A and B respectively, to measure the gravitational potential energy.
2lA + lC = l
2sA = -sB
sA = -3/2 = -1.5m
2vA = -vC

Conservation of Energy-
T1 + V1 = T2 + V2
0 + 0 = (1/2)(10)vB2 + (1/2)5(-vB/2)2 + 5(9.81)1.5 -10(9.81)3
vB =