Final answer:
The speed of the motor is 1750 rpm, the rotor frequency is 57.6 Hz, the speed of rotation of the rotor current wave relative to the rotor surface is 57.6 Hz, and the speed of rotation of the rotor current wave relative to the stator surface is -2.4 Hz.
Step-by-step explanation:
(a) The speed of the motor can be calculated using the formula: speed = (120 * (1 - slip)) / (number of poles * frequency). In this case, the speed = (120 * (1 - 0.04)) / (4 * 60) = 1750 rpm.
(b) The rotor frequency can be calculated using the formula: rotor frequency = frequency - slip * frequency. In this case, the rotor frequency = 60 - 0.04 * 60 = 57.6 Hz.
(c) The speed of rotation of the rotor current wave relative to the rotor surface is equal to the rotor frequency. So, in this case, it is 57.6 Hz.
(d) The speed of rotation of the rotor current wave relative to the stator surface is equal to the difference between the rotor frequency and the synchronous speed. So, it is equal to 57.6 Hz - 60 Hz = -2.4 Hz.