A rectangular metal plate has dimensions of 10 cm x 20 cm. A thin film of oil separates the plate from a fixed horizontal surface. The separation between the rectangular
plate and the horizontal surface is 0.2 mm. An ideal string is attached to the plate and passes over an ideal pulley to a mass m. When m = 125 gm, the metal plate moves at constant speed of 5 cm/s across the horizontal surface. Then the coefficient of viscosity of oil in dyne-s/${\mathrm{cm}}^2$ is (Use g = 1000 cm/${\mathrm{s}}^2$)