If the net electric potential at the origin is zero, what is q?

Question

A point charge of +4.0 μC is placed on the negative x–axis 0.20 m to the left of the origin, as shown in the accompanying figure. A second point charge q is placed on the positive x–axis 0.30 m to the right of the origin.  

If the net electric potential at the origin is zero, what is q?

(A) +9.0 μC 

(B) +6.0 μC 

(C) 0 

(D) –6.0 μC 

(E) –9.0 μC

Answer 1

The correct option is: (D) –6.0 μC 

Explanation:

If V = 0 and V = ΣkQ/r then q must be negative and (+4 μC)/(0.2 m) = q/(0.3 m)