# Electric Force between glass ball and rubber ball

## Homework Statement

What is the electric force between a glass ball with 3.5 µC of charge and a rubber ball with -5.0 µC of charge when they are separated by 5 cm?

## Homework Equations

Colombs Law:
F(electric)=K((q(1)*q(2))/r^2)
K=8.99E9

## The Attempt at a Solution

This seems like a simple plug in problem but I'm having a little trouble.

First i get the elementary charges of both the glass and rubber balls
so 1.6E-19*3.5=5.6E-19 for q(1)
and 1.6E-19*5=8E-19 for q(2)

So i plug in the numbers i know and get:
F(electric)=8.99E9(((5.6E-19)*(8E-19))/(.005^2))=-1.611E-22

I plug this into the program my school uses for physics homework and it tells me im wrong.

Can you see where im doing something wrong? please any help is appreciated.

## Answers and Replies

hage567
Homework Helper
First i get the elementary charges of both the glass and rubber balls
so 1.6E-19*3.5=5.6E-19 for q(1)
and 1.6E-19*5=8E-19 for q(2)
I don't understand why you did this. All you need to do is convert the 3.5 from microcoulombs to coulombs. Coulombs is the unit for charge.

F(electric)=8.99E9(((5.6E-19)*(8E-19))/(.005^2))=-1.611E-22

5 cm is not equal to 0.005 m. Check your conversion again.