Question

The net force on the 1.0 nC charge in the figure is zero. What is q?
Here is the figure
http://session.masteringphysics.com/problemAsset/1169215/1/jfk.Figure.20.P53.jpg

Answer 1

Force between two charges is given by Coulomb's law,\[F = \frac{Kq_1q_2}{R^2}\]where q_1 and q_2 are the charges and the separation between them is R. Here K is a constant \[K = 8.995\times 10^9 \frac{Nm^2}{C^2}\]The key idea for solving the question is that like charges repel each other and unlike charges attract each other. So each of the charges is repelling the 1nC charge resulting in the net force being zero. STEP I) Find the distances between 1nC charge and the other charges; you'd have to use Pythagoras theorem to do this. STEP II) the forces between the 1nC charge and the 2nC charges need to be resolved into their components. STEP III) Equate the net force in the Y direction to zero, and solve for the value of q.