# Force of 2 Point Charges

1. Jul 4, 2006

### therealkellys

I've been working on the following problem but when I try my answer online, it keeps coming up as incorrect. A charge Q1=-9.4 C is 4.8 m from a charge Q2 = 3.6 C. What is the magnitude of the electrostatic force on Q1?

I'm pretty sure for this its just Coulomb's Law so:
F = (k(Q1*Q2))/r^2
F = ((8.9876*10^9)(-9.4*3.6))(4.8^2)
F ~ 1.32 * 10^10 N
Taking into account sig. figs, my final answer is 1.3*10^10 N. \

However, this keeps coming up as incorrect. Am I overlooking something? Thanks in advance for the help!

2. Jul 4, 2006

### nrqed

Sounds right to me. Are you sure that the charges are given in Coulombs (and not microcoulombs or nanocoulombs)? Other than that, I can't see anything wrong.

Patrick

3. Jul 4, 2006

### therealkellys

Yep, I just looked it over again and all charges are given in Coulomb's. I think I might email my professor to see if he can look it over. Perhaps its a bug in the online grading system? I'm fairly confident in my answer. Thanks for looking it over!

4. Jul 4, 2006

### nrqed

You are welcome. Yes, it might be a big. Or maybe the system is expecting an answer with 3 sig figs (even though the answer should really have only two sig figs). But your answer is correct.

Best luck!

Patrick