having trouble with pith ball experiment....

Question

anonymous · Answer

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anonymous · Answer

attachment

anonymous · Answer

really bad drawing, but i got the first part, finding the force of gravity and number of electrons.  then it asks to draw a free body diagram, which i did (it looks better in my notes) and asks to calculate the coulomb force.  i have that f=k*q1*q2/r^2, but am i using the gravitational force here or something else?  i'm guessing something else since the next step is 3.	How does the gravitational attraction between the two pith balls compare to the electrostatic force? Calculate the ratio of Felectr / Fgrav.

anonymous · Answer

The gravitational attraction between the two pith balls can be calculated with an equation similar to finding the electrostatic force:
$$F _{g}=\frac{ GM _{1}M_{2} }{ r^{2}}$$

anonymous · Answer

Use this equation and find the ratio between the electrostatic force and the gravitational force to find your answer

anonymous · Answer

yes, i got that in part 1.  it's 2.308*10^-17.  i don't know how to do the second part in order to do the third part.  that's why i asked for help on finding the other force.