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uniidiot
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Homework Statement
The centre of a small sphere carrying a positive charge of 1.0 x 10^-8 C is fixed at 3cm above the centre of a small conducting ball, which had a negative charge and a mass of 0.05g. If the ball remains suspended, what charge does it have?
Answer is [ 4.9 x 10^-9]
but i can't seem to get that answer
Homework Equations
The Attempt at a Solution
Because the ball is suspended i take it that the force between the two charged bodies must be equal but opposite to the force due to gravity so:
F = mg
F = 0.05 x 9.8 = 0.49
F = (1/(4 x pi x epsilon 0)) x ((Q1 Q2) / r^2)
(1/(4 x pi x epsilon 0)) = 9 x 10^9
F = 9 x 10^9 x (Q1 Q2 / r^2)
Q2 = 9 x 10^9 x (Q1 / (r^2 x F)
Q2 = 9 x 10^9 x (10^-8 / (3^2 x 0.49)
Q2 = 20.4
please help