A 15-hp 230-V 1800 r/min shunt dc motor has a full-load armature current of 60 A when operating at rated conditions. The armature resistance of the motor is RA = 0.15 2, and the field resistance Rr is 80 the rated speed 1800 rpm. The adjustable resistance in the field circuit Radj may be varied over the range from 0 to 200 2 and is currently set to 90 2. Armature reaction may be ignored in this machine. The magnetization curve for this motor, taken at a speed of 1800 rpm is given in tabular form below: E (V) 8.5 153 195 221 223 242 I (A) 0.0 0.821 1.1 1.35 1.44 2.875 (a) What is the speed of this motor when it is running at the rated conditions specified above? (b) The output power from the motor is 15 hp at rated conditions. What is the output torque of the motor? (c) What is the efficiency of the motor at rated load? (d) What range of no-load speeds is possible in this motor, given the range of field resistance adjustments available with Radj?