Question

Two blocks of masses m1=1.7 kg and m2=3.1 kg are put on a frictionless horizontal surface. A spring of stiffness k=950 N/m and negligible mass is placed between the blocks and they are pushed together to compress the spring by distance d=28 cm from its equilibrium length. The configuration is fixed by a cord that holds the blocks. When the cord is burned, the blocks move in opposite directions. Calculate the speed of the first block.