Question

There is a repulsive force between two charged objects when

Answer 1

Answer: Both objects have charges of the same sign

When two electrically charged bodies come closer, appears a force that attracts or repels them, depending on the sign of the charges of this two bodies.

This is stated by Coulomb's Law:

"The electrostatic force $F_{E}$ between two point charges $q_{1}$ and $q_{2}$ is proportional to the product of the charges and inversely proportional to the square of the distance $d$ that separates them, and has the direction of the line that joins them"  

Mathematically this law is written as:  

$F_{E}= K\frac{q_{1}.q_{2}}{d^{2}}$

Where $K$ is a proportionality constant.

Now, if $q_{1}$ and $q_{2}$ have the same sign charge (both positive or both negative), a repulsive force will act on these charges.