Answer to Question #161268 in Physics for Desmond

Question

Two charged particles are 8.45 cm apart. They are moved and the force on 

each of them is found to have tripled. How far are they now?

Answer 1

The force between two charges can be written as follows:

$$F=\dfrac{kq_1q_2}{r^2}.$$

If the force is tripled we get the next formula:

$$3F=\dfrac{kq_1q_2}{r_{new}^2}.$$

Let's divide second equation by first equation:

$$\dfrac{3F}{F}=\dfrac{r^2}{r_{new}^2},$$ $$r_{new}=\sqrt{\dfrac{r^2}{3}}=\sqrt{\dfrac{(8.45\ cm)^2}{3}}=4.88\ cm.$$