College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 45

A motor has coils with a resistance of 30 and operates from a voltage of 240 V. When the motor is operating at its maximum speed, the back emf is 145 . Find the current in the coils (a) when the motor is first turned on and (b) when the motor has reached maximum speed. (c) If the current in the motor is 6.0 A at some instant, what is the back emf at that time