Question

1) Two positive charges q1=q2=2.0uc are located at x=0, y=0.30m, respectively. what are the magnitude and direction of the total electric force that q1 and q2 exert on a third charge Q=4.0 uc at x=0.40m, y=0?

2) suppose that charge q2 in question no 1 were (-2.0)uc in this case, the total electric force on q would be 1) in the positive x-direction; 2) in the negative x-direction; 3) in the positive y-direction; 4) in the negative y-direction; 5) zero; 6) none of these.

Answer 1

Since the two charges are located at the same point, they can be taken as one charge and hence we take it as 2+2 = 4uC.
Distance between these charges and the third charge.
$$\begin{gathered} \sqrt{(0-0.4{)}^2+(0.3-0{)}^2} \\ =0.5m \\ AsperColoumb\text{'}sLaw, \\ F=\frac{K(q_1+q_2)q_3}{r^2} \\ K=9\times {10}^{9}N \\ {q}_1+q_2=4\times {10}^{-6}C \\ {q}_3=4\times {10}^{-6}C \\ F=\frac{9\times {10}^9\times (4\times {10}^{-6}{)}^2}{(0.5{)}^2} \\ =0.576N \end{gathered}$$




In the second case it will be zero.