A single disc clutch with both the sides effective is used to run a machine through a shaft rotating at a uniform speed of 240 rpm. The coefficient of friction is 0.25. The inner and outer diameters of the disc are 120 mm and 240 mm, respectively. Maximum intensity of pressure is 120 kN/m. The moment of inertia of the rotating parts of the machine is 7 kg.m. Assume uniform wear theory. The time to attain the full speed by the machine is (a) 0.4 sec (c) 1.4 sec (b) 1 sec (d) 2.6 sec