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Two pith balls are free to float in space. If only gravitational and electrical forces are acting, and the balls have identical masses and charges (q = 4e), find the mass of the balls if they are moving at constant velocity.

I'm pretty sure that there is something I'm missing because when I try to solve for the mass, there are just too many variables to work with. Here's my work:

http://img291.imageshack.us/img291/2433/unsolvablemg8.png [Broken]

Known values:

k = 9.0 x 10^9 Nm²/C²

G = 6.67 x 10^-11 N /m²kg²

q = 4(1.60 x 10^-19 C)

Otherwise, there are 3 variables missing if we solve for m ...

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# Coulumb's Law Question

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