Question

Given: Q1 = +20 µc = 2.0 x 10-5 C

Q2 = +30 µc = 3.0 x 10-5 C

K = 9.0 x 109 N·m2/C2
r = 3.0 m

Determine F.

_____ N

2.0 x 10-10
1.8
0.60
6.7 x 10-11

Answer 1

The answer is: [C]: 0.60 N .
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Explanation:
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We use the formula / equation for "Coulomb's Law";
to get the answer, in "N", ("Newtons") :
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F = (k * q1 * q2) / r² ;
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and plug in our values that are given in the problem to solve:
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F = (k * q1 * q2) / r² ; (Plug in the values): to get:

= { [(9.0 * 10⁹ N·m² ) / C² ] * (2.0 * 10⁻⁵ C) * (3.0 * 10⁻⁵ C) } / { (3.0 m)² } ;
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= {9.0 * 10⁹ * 2.0 * 10⁻⁵ * 3.0 * 10⁻⁵ } / { (3.0²) } N ;
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{Note: "N" is the value in "Newtons", which we want.
The other units "cancel out" to "1".
Note that anything multiplied by "1" equals that same value.
Note that anything divided by "1" equals that same value.}. We shall retain the "2" significant figures in our final answer;
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So we have:
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F = {9.0 * 10⁹ * 2.0 * 10⁻⁵ * 3.0 * 10⁻⁵ } / { (3.0²) } N ;
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F = (5.4 / 9.0) N ;
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F = 0.60 N ; which is: Answer choice: [C].
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Answer 2

6.7 x 10-11....Have a good day with a big fat A+