A rotating furnace has been developed recently to give a rough parabolic curve to molten glass. This makes the manufacture of very large telescope mirrors easier and more economical than ever before. The largest mirror made in this furnace to date has a radius of 4.2 m. While in the furnace, the centripetal acceleration of the molten glass for this mirror was 2.13 m/s^2. What was the tangential speed at the edge of the molten glass?. Single line text.