A 15hp 220V 2000rpm separately excited dc motor controls a load requiring a torque ofτL=45N·mat a speed of 1200rpm. The field circuit resistance isRf = 147?, the armature circuit resistance isRa=0.25?, and the voltage constant of the motor isKv=0.7032V/A-rad/s. The field voltage is Vf = 220V. The viscous friction and no-load losses are negligible. The armature current may be assumed continuous and ripple free. Determine the back emf, Ea;