answer is 'c'

Solution:

Force on charge q at A:

(i) Due to B, f = kq ×

r2

q

or f=

r

2

kq

2

along BA

(ii) Due to C, f=

r

2

kq

2

along CA

∴ Resultant force = F

F

2

=f

2

+f

2

+2f×f×cos60

∘

F

2

=2f

2

+

2

2f

2

×1

=3f

2

or F=

3

f

or Resultant force =

3

r

2

kq

2

Solution Image