Calculating Charge Using Coulomb's Law

[jaxtar]

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?

Homework Equations

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.

 

[Feldoh]

It's radius squared right?

 

[jaxtar]

It's radius squared right?

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

 

[Feldoh]

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

 

[jaxtar]

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.

 

[diazona]

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...

 

[jaxtar]

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!