(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A plastic sphere with a positive charge of 4.8 x 10^-19 C is held stationary in a gravitational field of strength 9.8 m/s^2 by an electric field of strength 1.2 x 10^5 N/C. What is the force of gravity on the sphere?

2. Relevant equations

F_e=qE=kQq/r^2

F_g=mg=GMm/r^2

g=GM/r^2

3. The attempt at a solution

I think the only way to find the force of gravity is to find the mass of the sphere first. Since r^2=kQ/E, g=GM/(kQ/E)=EGM/kQ. So M=gkQ/EG

M=(9.8 m/s^2)(9.0 x 10^9 N x m^2/C^2)(4.8 x 10^-19 C)/(1.2 x 10^5 N/C)(6.67 x 10^-11 N x m^2/kg^2)=5.3 x 10^-3 m

If this mass is the mass of the sphere and not some other random object, then the number can be substituted into F_g=mg

F_g=(5.3 x 10^-3 m)(9.8 m/s^2)=5.2 x 10^-2 N

If M isn't the mass of the sphere, then I'm completely wrong, but that's the only solution I've been able to come up with. Can anyone tell me if I'm right?

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Using electric force to find the force of gravity

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