A 4:0-kg block (A) is pushed against a horizontal light spring with constant k = 4:0 104 N/m. When the
spring is compressed 4:0 cm from its relaxed length, the block is released. Block A then slides across a
horizontal frictionless surface and collides elastically with another block B (5:0 kg) that was initially at
rest. What is the nal velocity of each block?