# Rearranging Coulomb's Law

## Homework Statement

When a -9.0 micro-coulomb charge is placed 0.12 cm from a charge q in a vacuum, the force between the 2 charges is 850 N. What is the value of q?

F = kq1q2/r2

## The Attempt at a Solution

q2 = Fr2/kq1
q2 = (850 N)(0.0012 m2)/(9.00 x 109 Nm2/C2)(-9.00 x 10-6 C)
q2 = -1.22 x 10-18 C

My question is am I doing this right? The answer that my book gives is 1.5 x 10-8 C.

Last edited:

Related Introductory Physics Homework Help News on Phys.org

Yes it is sorry I corrected my work above! Thanks!

Well since you now (correctly) squared the radius, what do you get as an answer?

Well since you now (correctly) squared the radius, what do you get as an answer?
The answer that I get is -1.22 x 10-18 C. When I worked the question I had squared the radius.

Last edited:
diazona
Homework Helper
Well, the answer I get is the same one your book gives, so you're probably doing something wrong with the math. I'm not sure where that 10-18 is coming from...

Thanks for all your help! It was me trying to put too much info into my calculator at once. If I break it up figure out the top then figure the bottom and divide I get the right answer except mine is negative.

Thanks again!