Electric Forces Homework: Calculate Two Point Charges Using Coulomb's Law

AI Thread Summary
Two point charges are 3 m apart with a combined charge of 20µC and repel each other with a force of 0.075 N. The relevant equation is Coulomb's Law, F = k(q1*q2)/r^2. Participants are struggling with how to manipulate the equations to find the individual charges, specifically needing to use both q1*q2 and q1+q2 = 20. A suggestion is made to solve the two equations simultaneously, possibly using substitution. The discussion emphasizes the importance of correctly applying the equations to bridge the gap between the two unknowns.
dwn
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Homework Statement



Two point charges are 3 m apart and their combined charge is 20µC. If they
repel each other with a fore of 0.075 N, what are the two charges? Ans: 15 μC and 5μC  

Homework Equations



F=k(q1*q2)/r^2

(could someone mention in their response how we use the math text in our posts, so that I can make it more convenient for the reader)

The Attempt at a Solution



I'm really not so sure where to begin here, but I made a few attempts by manipulating both q2 and q2. I will post one of them below:

9*109 (q1+q2)/32=0.075N
 
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dwn said:
F=k(q1*q2)/r^2
Good.

(could someone mention in their response how we use the math text in our posts, so that I can make it more convenient for the reader)
Check out the FAQ, under "SITE INFO/Frequently Asked Questions" at the top of every page.

The Attempt at a Solution



I'm really not so sure where to begin here, but I made a few attempts by manipulating both q2 and q2. I will post one of them below:

9*109 (q1+q2)/32=0.075N
The one mistake you made was to use q1+q2 instead of q1*q2.

The second equation you'll need is q1+q2 = ??
 
I tried that in one of my attempts, but I don't see the "bridge" between the two equations.

If I solve Coulombs equation for q1*q2, I don't see where I'm supposed to plug in q1+q2 = 20 into the other equation...?
 
dwn said:
I tried that in one of my attempts, but I don't see the "bridge" between the two equations.

If I solve Coulombs equation for q1*q2, I don't see where I'm supposed to plug in q1+q2 = 20 into the other equation...?
You'll have two equations and two unknowns. Solve them simultaneously, using any method you like. (Such as substitution.)
 

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