Question

Two identical small conducting balls B₁ and B₂ are given –7 pC and + 4 pC charges respectively. They are brought in contact with a third identical ball B₃ and then separated. If the final charge on each ball is –2 pC, the initial charge on B₃ was

Two small metal blocks (X and Y) of the same mass m are placed on an insulated frictionless surface such that both of them are at the same distance from the edge of the surface as shown in the image below. The charge on block X is +100 Q and that on Y is +50 Q. The two blocks are held in position by an external force.