If you were to build a motor using only permanent magnets, its rotor might spin briefly but it would soon come to a stop as friction turned its energy into heat. To keep the rotor turning, you must replace one of the magnets with an electromagnet and control that electromagnet so that it always does work on the rotor, increasing its energy. To do work on the rotor, the electromagnet should be adjusted so that it always
A)	attracts each magnet that moves toward it and repels each magnet that moves away from it.
B)	attracts each magnet that moves toward it and attracts each magnet that moves away from it.
C)	repels each magnet that moves toward it and repels each magnet that moves away from it.
D)	repels each magnet that moves toward it and attracts each magnet that moves away from it.
Answer:A
If you were to build a motor using only permanent magnets, its rotor might spin briefly but it would soon come to a stop as friction turned its energy into heat. To keep the rotor turning, you must replace one of the magnets with an electromagnet and control that electromagnet so that it always does work on the rotor, increasing its energy. To do work on the rotor, the electromagnet should be adjusted so that it always
A)	attracts each magnet that moves toward it and repels each magnet that moves away from it. B)	attracts each magnet that moves toward it and attracts each magnet that moves away from it. C)	repels each magnet that moves toward it and repels each magnet that moves away from it. D)	repels each magnet that moves toward it and attracts each magnet that moves away from it.