Final answer:
The charge on object A becomes positive after it is contacted by the positively charged aluminum pop can, which was charged by induction using a negatively charged rubber rod.
Step-by-step explanation:
The subject of this question is the charging by induction and the nature of electrostatic charges in Physics. The process begins with a rubber rod gaining a negative charge due to its greater electron affinity when compared to animal fur (it becomes negatively charged when rubbed with animal fur). The rod is then brought near to an aluminum pop can without touching it, inducing a redistribution of charges, with positive charges being attracted to the rod. If the far end of the can is grounded (even momentarily), the free electrons in the can have a path to leave the can, resulting in a net positive charge on the can. Once the rod is removed, the can retains this positive charge. Finally, when the can is brought into contact with object A, it would transfer some of its positive charge to the object, making the charge on object A positive.