Two upright metal rails are $0.14$ m apart and are joined at the top, so the loop they form has a resistance of $0.038\ \Omega$. A crossbar of mass $12$ g is released and slides down them. A horizontal field of $0.57$ T is at right angles to the plane of the rails. What steady speed does the crossbar reach? Take $g = 9.8\ \text{m/s}^2$.