This is probably child's play for most of you, but a guy like me struggles to understand basic concepts. A kick in the pants to set me off in the right direction would be greatly appreciated.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

How far must the point charges q_1 = 7.60 microCoulombs and q_2 = -24.0 microCoulombs be separated for the electric potential energy of the system to be -110 J?

2. Relevant equations

E=F/q

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

k=8.988810^9 (Nm^2)/(C^2)

Volt = N/C

W=Fr

r= distance in this case

3. The attempt at a solution

Honestly, I'm not quite sure where to start. Not sure which formula I'm supposed to use. I gave it a try anyway, though. Coulomb's Law seems perfectly reasonable until I realize that I don't have a value for distance. All the same, I multiplied 8.988E9 by 7.6E-6 and 24E-6 and assumed my force would equal 1.63941r^2 N.

Then, since work is measured in joules and so is potential energy, I tried to use the formula W=Force x distance (and I still don't know the distance), giving me something like 1.63941r^3 Joules.

And if I wasn't already lost, I notice that electric potential is supposed to be measured in volts. But since the question doesn't ask for volts, all that's left is for me to solve for r.

I try to solve for r by means of 1.63941r3=110, which gives me 4.06 (4.1) meters.

Since the question wants the answer in cm, I used 4.1x10^2 cm.

Obviously, I got the answer wrong.

It's no surprise, seeing as how I'm just sort of drowning in a vast ocean of numbers.

Can I get a metaphorical life preserver?

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# Homework Help: Point charges and potential electric energy

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