1. The problem statement, all variables and given/known data How much work must be done to carry a +2.3 X 10^-3 C charge from 65 cm to 15 cm? From the question: q=+2.3 X 10^-3 C r1= 65 cm = 0.65 m (these must be converted to metres) r2= 15 cm = 0.15 m k= 9.0 X 10^9 Nm^2/C^2 W=? W=∆Ee ∆Ee=q∆V (I'd just like to say that this question is from grade 12 physics) 2. Relevant equations Ok here’s the formulas i've been given. Fe=Kq1q2/r^2 E=kq/r^2 E=Fe/q Ee=Kq1q2/r ∆Ee=Kq1q2(1/r2 - 1/r1) ∆Ee=q∆V V=Kq/r V=Ee/q E=∆V/r W=∆Ee=q∆V q=Ne Where K is coulombs constant (I think that’s what it’s called) K=9.0 X 10^9 Nm^2/C^2 I hope the people who try to help know what those formulas are already. If not I can tell you what they are. 3. The attempt at a solution From the question: q=+2.3 X 10^-3 C r1= 65 cm = 0.65 m (these must be converted to metres) r2= 15 cm = 0.15 m k= 9.0 X 10^9 Nm^2/C^2 W=? W=∆Ee ∆Ee=q∆V So I thought ok, so I need to find ∆V now. Rearranging ∆Ee=q∆V for ∆V. ∆V=∆Ee/q What equations have ∆V in them? ∆Ee=q∆V (well we are trying to find ∆Ee already) E=∆V/r (oh so I need to find E now) What equations have E in them? E=kq/r^2 (can't use this equation thought because there is two radius's, r1 and r2, and this equation only has one. E=Fe/q (oh so now i need to find Fe) What equations have Fe in them? Fe=Kq1q2/r^2 (but I can’t use that equation because I only have one q) E=Fe/q (can’t use this equation either because I was trying to find Fe to find E from the other equation) Then I thought wait there’s also the equation ∆Ee=Kq1q2(1/r2 - 1/r1), but again the question only gives one q. I could only use this equation if q=q1 and q2=q1, but I cannot be sure of that. It’s like a circle that brings me to nowhere so I am stumped. Someone from another website told me this: "As long as you move the charge in a space where no electric field is detected the work is equal to zero. in order to give your problem a physical meaning you should precise the electric field in which the charge moves, which could be generated by another point-like charge or an uniform electric field." The problem is the question gives no other point charge, so I don't know what to do. I am stuck at this point. If you can help I would greatly appreciate it. This question is from a "take home quiz" from my grade 12 physics class. It is due on Monday April 28, 2008, 3 days from today, so if anyone could help sooner than later would be better. Thanks.