2-A piston of 7.8 cm diameter rotates concentrically inside a cylinder 8.0 cm diameter. The length of the piston and the cylinder is 10 cm. The space between the cylinder and the piston is filled with oil film having viscosity 2.4 poise. Find the speed of rotation in r.p.m. of the piston if a torque of 1.4 N.m is applied.