Okay, haven't done physics in years, let's see if I remember this.
So Coulomb's Law states that

so if we double the charge on

and double the distance to

we plug these into the equation to find
<span>

</span>
So we see the new force is exactly 1/2 of the old force so your answer should be

if I can remember my physics correctly.
Explanation:
zoom I'd - 9038735228 pwd -97cEeT I m getting bored wanna come for intresting talk
Same speed, because mass is neglected. The things that affect the speed are the distance and speed of the rock.