# phYsics

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Two identical objects each hold a net charge of q = 8e. If the gravitational force between the two objects exactly cancels the electrostatic force between the objects, what is the mass of each object?
Where G: 6.67E-11
Ke=8.99E9

I know the equation is
m=sqrt(ke*q^2/G)
yet when I plug everything in I got 2.52E11 which is incorrect.

• phYsics -

G M^2/R^ = Ke 64 e^2/R^2

M^2 = 64 Ke e^2/G
M = 8e sqrt(Ke/G)

You seem to be using the right formula, but I get a different numerical answer.

Are you sure you are using the right electron charge (e)?

• phYsics -

Oh, you mean the 'e' in the 8e might stand for 8 times electron charge of 1.60217646E-19 coulombs? I was doing it as 8 times e(the mathematical constant 2.71828183)

• phYsics -

Yes, e is the electron charge. You are comparing electrostatic and gravitational forces

• phYsics -

Thank you! I should have known that, guess its getting late :)

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