# Homework Help: Net force on charges found to be zero

1. Sep 3, 2006

### eltel2910

I'm having trouble understanding some of these basic electrostatic priciples and my book isn't much help. I've put them in a true/false format. If I could get at few answers, it would really help me understand this.

A positive point charge +q is placed at point p to the right of two charges, A and B. The net force on the +q charge is found to be zero. Which of the statements below are true?

A-----------B-----------P
++++++++++++++++++++q

True or False -- The magnitude of the charge A must be smaller than B.

True or False -- Reversing the sign of +q to -q would make the force on it nonzero.

True or False -- B must have the same sign as A and be less in magnitude.

True or False -- B must have the opposite sign from A and be less in magnitude.

True or False -- Either A or B must be positive.

2. Sep 3, 2006

### arunbg

Welcome to PF eltel.
What are your thoughts on how to go about solving the questions ?
Start from the basics, namely Coulomb's law .

3. Sep 3, 2006

### borisleprof

I eltel,
you must analyse two cases:
A negative then B must be positive so that the net force be zero on p.
A positive then B must be negative....
Then use Coulomb's law to complete your reasoning.