Spring Question...help?

Question

Block A has mass 1.00kg , and block B has mass 3.00kg . The blocks are forced together, compressing a spring S between them; then the system is released from rest on a level, frictionless surface. The spring, which has negligible mass, is not fastened to either block and drops to the surface after it has expanded. Block B acquires a speed of 1.20m/s .

What is the final speed of block A?
How much potential energy was stored in the compressed spring?

Please and thank you.

Answer 1

Momentum is conserved, so
3*1.2=1*v
v=3.6 m/s in the opposite direction as B

The energy is
.5*3*1.2^2+.5*1*3.6^2

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