Referring to worked example 1.4, what is the net force on (i) q1 (ii) q2

Let's solve this problem using Coulomb's Law. The problem refers to "Worked Example 1.4" which describes the charges and their distances from q₃. We need to determine the arrangement of the charges first.

From Worked Example 1.4:
q₁ = +1.0 nC = +1.0 × 10⁻⁹ C
q₂ = -3.0 nC = -3.0 × 10⁻⁹ C
q₃ = +5.0 nC = +5.0 × 10⁻⁹ C

q₁ is at a distance of 2.0 cm from q₃.
q₂ is at a distance of 4.0 cm from q₃.

A common interpretation for this setup,