two blocks of masses m and 3 m are placed on a horizontal, frictionless surface. a light spring is attached to one of them, and the blocks are pushed together with the spring between them. m 3m m 3m before after (a) (b) v a cord holding them together is burned, after which the block of mass 3 m moves to the right with a speed of 2.06 m/s. what is the speed of the block of mass m? answer in units of m/s