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# Checking the solution

The answer for the problem https://brilliant.org/assessment/s/mechanics/409790/ was given to be +1.386 but I think that the answer should be -1.386. The potential energy comes out to be +1.386 . Hence the work done should be -1.386 J. Please explain.

Note by Saurabh Dubey
4 years, 6 months ago

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Saurabh,

You have a sign issue with your potential energy. Consider one of the negative charges. You can use the sum rule in the problem to then compute the electric potential V, which winds up positive. The potential energy, which is -qV is negative. Intuitively this makes sense, as the closest charges to any given charge are of opposite sign. Therefore any given charge will be attracted into the chain, i.e. a lower potential energy. Staff · 4 years, 5 months ago

Now i got it sir. The potential energy is -ve hence the work done should be +ve. Thank you sir. · 4 years, 5 months ago

Saurabh...can you give me the title of the problem? Once I find it, I am happy to help you out. Staff · 4 years, 6 months ago

Sure sir, its "Breaking the chain". Appeared around three weeks ago. · 4 years, 5 months ago

well, the page says 'This solvable does not exist'