Duas partículas eletrizadas com cargas iguais a +25uC estão colocadas a 1,0m uma da outra, no vácuo, onde a constante eletrostática vale 9.10^9 unidades do Sistema Internacional. Não havendo influência de outras cargas, determine: a) a intensidade do campo eletrostático que cada carga cria no ponto P, situado a meia distancia entre elas;
b) a forca resultante que age numa carga de prova de +2,0uC colocada em P.

it is very well related to a lot of things but with my limited knowledge i can confidently say that the answer is space.

fgravity=10x10=100n case 1

fgravity=30x20=600n case 2

6 times more

the answer is b, have negligible mass

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.