# Homework Help: Magnitude of the electrostatic force

1. Sep 6, 2012

### slk011

Hello,

Any help woould be wonderful!

Identical point charges Q are placed at each of the four corners of a rectangle measuring 2.35 m by 3.05 m. If Q = 26.9 μC, what is the magnitude of the electrostatic force on any one of the charges?

i dont even know where to start.... HELP!

2. Sep 6, 2012

### CAF123

Have you come across Coulomb's Law?$$F = k\frac{Q_1Q_2}{r^2}$$
You need to find the forces acting on any one of the charges. These forces will be from the other 3 charges and because they are identical, the forces acting on your chosen charge will be ones of repulsion.
You will need to set up a suitable coordinate system. This will allow you to deduce the directions of all force contributions.

3. Sep 6, 2012

### slk011

Yes we are learning the law right now. But i am not sure waht to do with the "m" given, do i add them all...? im so lost.

4. Sep 6, 2012

### CAF123

Definitely start by drawing a picture and set the origin of your axes at one of the charges. Then draw in all the forces acting on your chosen charge. Using your coordinate system, write vector equations for each force.
The 'r' in Coulomb's Law is the distance between two charges. This 'r' will need to be computed using Pythagoras for the charge diagonally opposite the one you chose.