1) Plate glass, initially at 520C, is cooled by passing air on both surfaces with an effective surface coefficient of 4.5W/m2.K. The temperature gradient in the glass shall be limited to 20K/cm during the cooling process, in order to minimize cracking in the glass. What is the lowest temperature of the air that shall be used? Thermal conductivity of glass is 1.4W/m.K. 2) The solar radiation incident on a steel plate 1.5ft square is 400Btu/h. The plate is 1.5 in thick and lying horizontally on an insulating surface, its upper surface being exposed to air at 90F. If the convective heat-transfer coefficient between the top surface and the surrounding air is 4Btu/h.ftF, what will be the steady-state temperature of the plate