A straight conductor parallel to the x-axis can slide devoid of friction on top of two horizontal conducting rails which are parallel to the y-axis and a distance of L = .2 m apart, in a vertical magnetic field of 1 T. A current of 20 A is maintained via the conductor. When a string is joined exactly at the center of the conductor and passes over the frictionless pulley, what mass m hanged from the string permits the conductor to be at rest?