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Old Sep 29th 2011, 05:46 PM   #1
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Electric force on a sphere

Problem: Two small plastic spheres each have a mass of 2.0 and a charge of -50.0. They are placed 2.0 apart.

Question:
By what factor is the electric force on a sphere larger than its weight?

Weight= 19.6 N
Electric Force would be = 8.99 x 10^9 * 5x10^-8/(.02)^2

Is this correct to begin? then how would I find the factor difference?
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Old Oct 3rd 2011, 01:35 AM   #2
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Not quite, notice that the mass is in grams and not in kilograms

But it's okay, now to get the factor, you are being asked how many times the electrostatic force is larger/smaller than the weight (or did the question mean the gravitational force and you understand it another way?).

So, bring down the weight to 1. That is, by how much do you have to divide the weight for it to become equal to 1? When you have got that value, divide the electrostatic force by that same value, and that will be your answer.

E.g.
Weight = 5 N
E. Force = 20 N

Value to divide weight to get 1 is 5 (5/5 = 1)
Thus, factor = (20/5 =) 4. So, the factor the electric force is 4 times larger than its weight.

But I will say it again, are you sure it meant weight, or did it mean the gravitational attraction between the two spheres?
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