Block A has mass 1.00 kg, and block B has mass 3.00 kg. The blocks are forced together, compressing a spring 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 1.10 m/s. a) What is the final speed of block A? Found this answer to be 3.30 m/s b) How much potential energy was stored in the compressed spring? - how do you find this answer??