Three balls are suspended from a ceiling by insulating strings. Balls A and B are found to attract each other and balls B and C are found to repel each other. From this we can conclude that balls A and C...

A) carry charges of opposite sign

B) carry charges of equal sign

C) have no charge

D) have charge that cannot be determined from the given information

Solution: D. Charges of opposite sign attract, charges of equal sign repel, and any type of charge attracts a neutral object (due to polarization). So A and B either carry charges of opposite sign or one of the two is neutral and the other charged. Since B and C repel, however, we know that B and C carry charges of equal sign. So there are two possibilities: A is either neutral or carries a charge of the opposite sign to that of B and C.