# Electric Forces with particles and Columbs law problem.

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1. Sep 19, 2015

### Toon

1. The problem statement, all variables and given/known data
Two particles, one with charge -7.13 × 10-6 C and one with charge 1.87 × 10-6 C, are 0.0284 meters apart. What is the magnitude of the force that one particle exerts on the other?
Two new particles, which have identical positive charge q3, are placed the same 0.0284 meters apart, and the force between them is measured to be the same as that between the original particles. What is q3?

2. Relevant equations
Fe=Kq1*q2 /r^2

3. The attempt at a solution
So for the first part. I got the answer right for the force which was 148.7 N. However for the second part, I tried doing Fe= kq3^2/r^2 and solved for q3. However I keep getting 3.6 x 10 ^-6 columbs and thats wrong according the my physics hw website. Any help where im going wrong?THanks!

2. Sep 19, 2015

### TSny

Could it be that you are not expressing your answer to the correct number of significant figures?

3. Sep 19, 2015

### Toon

thats what im thinking. However Ive tried diffrent ways of expressing the answer and its still wrong so im assuming my numbers might be off.

4. Sep 19, 2015

### TSny

What do you get to 3 significant figures?

5. Sep 19, 2015

### Toon

3.651 x 10 ^-6 but the answer is still wrong

6. Sep 19, 2015