Two charges of # -6 C # and # 4 C# are positioned on a line at points # -6 # and # 9 #, respectively. What is the net force on a charge of # -1 C# at # 1 #?
You have to use the superposition principle. The net force is the vector sum of all the external forces acting on the -1C charge.
To calculate the electrical attractive/repulsive forces, we use Coulomb's Law. Coulomb's Law states that the electrostatic force is directly proportional to the charge of each object and has an inverse-squared relationship with the distance between the 2 charges.
a.k.a. Coulomb's constant.
From the formula, we can see that whether the force is attractive or repulsive depends on whether we are dealing with unlike charges or like charges.
In this question, I assume that the distance is measured in meters, since it is not specified.
The force exerted by the -6C at -6 is given by the coulomb law,
Since the unlike charges repel, the force is directed towards the right.
The force exerted by the 4C at 9 is given by the coulomb law,
Since the like charges attract, the force is directed towards the right.
I recommend you to draw a diagram of the 3 charges to visualize it more clearly.
The sum of the 2 forces is