Final answer:
To determine the charges on two objects that repel each other, you can use a known charged object and observe its interaction with one of the objects.
Step-by-step explanation:
When two objects repel each other, it indicates that they have the same type of charge, either positive or negative. However, it is not possible to determine whether they are both positive or both negative solely based on the repulsion.
To determine the charges on the objects, you can use a known charged object, such as a charged rod, and bring it close to one of the objects. If the known charged object is positive and it is repelled from the object, then the object must also have a positive charge. Conversely, if the known charged object is attracted to the object, then the object must have a negative charge.