30 = 9,0*10^9*10^-5*q*10^4/36
q = 30*36/(9,0*10^9*10^4*10^-5) = 1,20*10^-6 Co = 1,20 μCo
127 = 9,0*10^9*q^2*10^4/4^2
q = √127*4^2/(9*10^9*10^4) = 4,75*10^-6 Co = 4,75 μCo
Hanno sicuramente lo stesso segno (non importa quale)
1,0 = 9,0*10^9*4*10^-11/d^2
d = √9,0*10^9*4*10^-11 = 0,60 m
F = 9,0*10^9*10^-11/0,5^2 = 0,36 N
Costante di Coulomb K in alcool etilico = 9*10^9/28 N*m^2/Co^2.
2,0*10^-4 = 9,0*10^9*q^2*10^4/(28*20^2)
q = √2,0*10^-4*28*20^2/(9*10^13) = 1,6*10^-7 Co
50 = 9*10^9*35*10^-12/d^2
d = √9*35*10^-3/50 = 0,08 m = 8 cm