Passage - IV: A perfectly plane house roof makes an angle theta with the horizontal surface. A flat square metal plate of side L rests over the roof. Each day temperature varies between day's high (T_1) and day's low (T_2). Coefficients of thermal expansions of roof and plate are alpha_(1) and alpha_(2) ( alpha_(2) gt alpha_(1) ) respectively. Coefficient of kinetic friction between plate and roof is mu_(k). Plate and roof are always in contact and both have same temperature at every instance of day. Because of difference in coefficients of thermal expansions, each bit of plate is moving relative to the roof, except for points along a certain horizontal line (called stationary line). The stationary line occupies no area, so we assume no force of static friction acting on the plate while the temperature is changing. When the temperature is raising, then distance of the stationary line from top edge of plate will be