Question

Two point charges, with charges q1 and q2, are each moving with speed v toward the origin. at the instant shown q1 is at position (0,
d.and q2 is at ( d, 0). (note that the signs of the charges are not given because they are not needed to determine the magnitude of the forces between the charges.) part a what is the magnitude of the electric force between the two charges? express f in terms of q1, q2, d, and ϵ0.

Answer 1

The force between two charged particles is Coulomb's force which is given by this formula:
$F_c=\frac{q_1q_2}{4\pi \varepsilon_0 r^2}$
Wher r is the distance between particles. In our case distance is simply diagonal of the square.
$r=\sqrt2 d$
So the final formula is:
$F_c=\frac{q_1q_2}{8\pi \varepsilon_0 d^2}$