A three-phase, 60-Hz, four-pole, 10-hp, 460-V (line-line, nns) induction motor has a full-load speed of 1746 rpm. Assume the torque-speed characteristic in a range of 0- 150% rated torque to be linear. It is driven by an adjustable-frequency sinusoidal supply such that the air gap flux is held constant. Plot its torque-speed characteristics at the following values of frequency f: 60, 45, 30, and 15 Hz