Problem on Conservation of energy

[scytherz]

Homework Statement

Two blocks, A and B (mA=50 kg and mB=100 kg), are connected by a string as
shown. If the blocks begin at rest, what will their speeds be after A has slid
a distance d = 0.25 m? Assume the pulley and incline are frictionless.

Homework Equations

K= .5mv^2
P=mgh
ke(initial) + pe(initial) = kef = pef

The Attempt at a Solution

.5mvi^2 + mghi = .5mvf^2 + mghf (at rest)
.5mvf^2 = -mghf
.5(50 kg) vf^2 = -100(-9.8)(.25sin37)
vf = 2.42 m/s which is wrong... where did i go wrong? the ans. is 1.51 m/s

 

[PhanthomJay]

You have your vf and vi mixed up, but beyond that, do not forget that both blocks have a change in their potential and kinetic energies.