Answer to Question #309232 in Physics for Justin

Question

Two charges are on the x-axis. Charge q1 = +25 nC is at x = 4.00cm while charge q2 = -75nC is at x = 7.00 cm,

Find the magnitude and direction of:

a.) the electric force that q1 exerts on q2; and

b.) the electric force the q2 exerts on q1.

Illustration:

Free-body diagram:

Answer 1

The Coulomb's law says

$$F=k\frac{q_1q_2}{r^2}\\ =9*10^9*\frac{25*10^{-9}*75*10^{-9}}{0.03^2}=0.019\:\rm N$$

(a) $F_{12}=0.019\:\rm N$ (directed toward negative x-axis)

(b) $F_{21}=0.019\:\rm N$ (directed toward positive x-axis)