Calculating voltage from multiple point charges

1. The problem statement, all variables and given/known data
A point charge 10 km in the air with a charge of 40 coulombs
A point charge 5 km in the air with a charge of -40 coulombs
A point chare 2 km in the air with a charge of 10 coulombs
-Find the electric potential due to these charges at a point which at a height of 8 km and on the vertical line passing through the charges.


2. Relevant equations
kq1/r1 + kq2/r2


3. The attempt at a solution

So I summed them up

v = k (40C/2000m - 40C/3000m + 10C/6000m) = 7.5E7

My question is, is do I need to convert km to m and was I correct in subtracting the negative 40 coulomb charge from the rest of the positive charges?
 

Delphi51

Homework Helper
3,407
10
Yes and yes. Looks good to me.
 

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