Charges in a Line Conceptual Question with picture

[PeachBanana]

Homework Statement

Two balls, one with charge Q1 = +Q and the
other with charge Q2 = +2Q, are held fixed at a
separation d = 3R as shown.

See picture.

Another ball with (non-zero) charge Q3 is
introduced in between Q1 and Q2 at a
distance = R from Q1.

See right below first picture.

• Which of the following statements is correct?

1. The force on Q3 can be zero if
Q3 is positive
2. The force on Q3 can be zero if
Q3 is negative
3. The force on Q3 can never be
zero, no matter what the (nonzero)
charge Q3 is.

Homework Equations

F = kq1q2/r

The Attempt at a Solution

I initially said two but then changed my mind because the +2Q charge will always exert a force on Q3 (although it may not be as strong). What do you all think?

 

[Saitama]

Find the net force in each case on charge Q3.