# Homework Help: Coulomb's law

1. Mar 31, 2012

### bobsmith76

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

see attachment

2. Relevant equations

3. The attempt at a solution

Do you see the step where they go from (1.35keq2)/a2

to 1.91keq2)/a2 ?

I can't get that step. To my mind. If you square 1.35 then take its square root, you get 1.35 not 1.91

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2. Mar 31, 2012

### RoshanBBQ

$$\sqrt{1.35^2 \left (\frac{k_e q^2}{a^2} \right )^2 +1.35^2 \left (\frac{k_e q^2}{a^2} \right )^2}$$
$$\sqrt{\left (\frac{k_e q^2}{a^2} \right )^2(1.35^2 +1.35^2) }$$
$$\frac{k_e q^2}{a^2}\sqrt{1.35^2 +1.35^2 }$$
$$\frac{k_e q^2}{a^2}\sqrt{(2)(1.35^2)}$$
$$\frac{k_e q^2}{a^2}\sqrt{2}1.35$$
$$\frac{k_e q^2}{a^2}1.91$$

3. Mar 31, 2012

### SammyS

Staff Emeritus

If you square 1.35 then multiply by 2, then take the square root of that result you do get 1.91, approximately.

4. Mar 31, 2012

### bobsmith76

Roshan,

Excellent answer. If only more math texts included as many steps as you do!!! I really appreciate it.