Coulomb's law for the magnitude of the force Fbetween two particles with charges Q and Q′separated by a distance d is |F| = K x (|QQ′|/d2), where K=1/(4π?0), and ?0=8.854×10^-12 C^2/(N⋅m2) is the permittivity of free space.
Consider two point charges located on the x axis: one charge, q1 = -15.0 nC, is located at x1 = -1.745 m ; the second charge, q2 = 31.0 nC , is at the origin (x=0.0000).
What is the net force exerted by these two charges on a third charge q3 = 52.0 nC placed between q1 and q2 at x3 = -1.120 m ?
Answer may be positive or negative, depending on the direction of the force.