One last physics problem have tried 3 times still cant get it?

Question

Problem:
http://img339.imageshack.us/img339/4518/phys2lh6.gif

Answer 1

The friction force =uN and work =uNh = mechanical energy lost

Answer 2

m1 = 4 kg
m2 = 7 kg
μ = 0.2
k = 9 N/m
g = 9.8 m/s²

At lowest point:
Work done by friction: A = μgm1 h
Potential energy of the spring Ps = ½kh²
Potential energy of the second block Pg = -gm2 h
Kinetic energy K = 0

Conservation of energy:
A + Ps + Pg = 0
μgm1 h + ½kh ² = gm2 h
μgm1 + ½kh = gm2

h = 2g(m2 - μm1)/k = 13.5 m

Answer 3

7kg+7kg+person sitting under the block coming down=blood bath