A light rigid metallic bar of rectangular cross section lies on a block of ice, extending slightly over each end. The width of the bar is 2 mm and the length of the bar in contact with the ice is 25 cm. Two equal masses, each of value M, are hung from the extending ends of the bar. The entire system is at atmospheric pressure and is maintained at a temperature of 7 -2 °C. What is the minimum value of M for which the bar will pass through the block of ice by "regelation?" The given data are that the latent heat of fusion of water is 80 cal/g, that the density of liquid water is 1 g/cm³, and that ice cubes float with -4/5 of their volume submerged.