# Physics problem on force of a charge

1. May 13, 2015

### Joshua Beyer

1. The problem statement, all variables and given/known data
Two point charges are on the x-axis. One charge, q1 = +10nC, is located at the origin, and the other charge, p2=-18nC is located at x = 9.0m

2. Relevant equations
a.) what is the force on q2(include direction)?
b.) what is the force on q1(include direction)?

3. The attempt at a solution
f=(k(q1q2)/r^2)
f=(9.0*10^9(10*18)/9^2)
K = coulomb's law = 9.0*10^9
I got 1.3122*10^14, but was told that was WAY wrong.

2. May 13, 2015

### TSny

HI, Joshua. Welcome to PF!

(1) Note that the charge is given in units of nC. You need to take into account the "n".
It's a very good idea to include units in your calculation and make sure that the units combine to give the correct unit for the force.

(2) Looks like you multiplied by 9^2 rather than divided by 9^2.

(3) "k" is Coulomb's constant, not Coulomb's law.

3. May 13, 2015

### OmCheeto

I believe the "n" in "nC" stands for "nano".