Question

What is the distance between two spheres, each with a charge of 2.5 x 10-6 c, when the force between them is 0.50 n?

Answer 1

In this case, Coulomb's Law applies:

F = 1/(4πε₀) · (Q₁Q₂/r²)

You can solve it for r:

r = √[1/(4πε₀) · (Q₁Q₂/F)]

Plugging in numbers:

r = √[1/(4π·8.85×10⁻¹²) · (2.5×10⁻⁶)²/0.50] 
  = 0.335m

The correct answer is: the two charges are 0.335m apart.