Rearranging Coulomb's Law

  • Thread starter jaxtar
  • Start date
  • #1
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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.
 
Last edited:

Answers and Replies

  • #2
1,341
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It's radius squared right?
 
  • #3
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It's radius squared right?
Yes it is sorry I corrected my work above! Thanks!
 
  • #4
1,341
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Well since you now (correctly) squared the radius, what do you get as an answer?
 
  • #5
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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:
  • #6
diazona
Homework Helper
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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...
 
  • #7
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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!
 

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