A 50 horsepower, 250 volts, 1200 rpm, separately excited dc motor has a rated armature current of 170 amps and a rated field current of 5 amps. When the rotor is blocked, an armature voltage of 12.2 volts produces the rated current and a field voltage of 250 volts produces the rated field current. At no load, with a terminal voltage equal to 240 volts, the armature current equals 13.2 amps, the field current equals 4.8 amps and the motor runs at 1150 rpm. Determine the efficiency of the motor on full load operation. (Assume a constant voltage drop of 2 volts at the brushes at all operating conditions.)