physics help??

Question

In Figure 9-61, block 1 (mass 1.6 kg) is moving rightward at 10 m/s and block 2 (mass 4.8 kg) is moving rightward at 2.8 m/s. The surface is frictionless, and a spring with spring constant of 1160 N/m is fixed to block 2. When the blocks collide, the compression of the spring is maximum at the instant the blocks have the same velocity. Find the maximum compression.

http://i175.photobucket.com/albums/w138/kacortez/hrw7_9-61.gif

Answer 1

Since momentum is conserved
1.6*10+4.8*2.8=(1.6+2.8)*v
v=6.69 when they move with the same speed
the delta KE is
.5*1.6*100+.5*4.8*2.8^2-.5*(1.6+2.8)*6.69^2
0.3528 j
this energy is in the spring
.5*1160*x^2=0.3528
solve for x
x=0.02 m

j