Answer :
The phenomenona of vectors proved.
What is vector?
vector is a quantity that has two independent properties magnitude and direction.
The electric force is given by coulumb's law
F = k q₁q₂ / r²
Let's apply newtons second law in particle 3
F = F₃₁ - F₃₂
F₃₁ = k q₃q₁ / r₃₁²
F₃₂ = k q₃q₂ / r₃₂²
Let's write the values they give us
q₁ = -4.0 10⁻⁶ C
x₁ = 0
q₂ = q₃ = + 8.0 10⁻⁶ C
x₂ = 4.0 m
x₃ = -4.0 m
We look for the distances
r₃₁ = x₃ -x₁
r₃₁ = -4.0 - 0 = -4.0 m
r₃₂ = -4.0 - 4.0 = -8.0 m
Let's write the force equation
F = k q₃ (q₁ / r₃₁² + q₂ / r₃₂²)
so let's calculate
F = 8.99 10⁹ 8 10⁻⁶ (4 10-6/4 2 - 8 10-6 / 8 2)
F = 71.92 10³ (1/2 - 1/8 )10⁻⁶
F = 26.97 10-3 N
None of the charge are on the axis and therefore there are no forces on this axis.
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