NEET 2020 Model Question Paper 1

The charge moves towards x-axis. Let at certain instant its position from point O is x.
Instantaneous resultant force acting over it is given as
FR=2F‌cos‌θ
=2

qQ

4πε0(a2+x2)

x

√a2+x2

FR=

2qQ

4πε0

x

(a2+x2)3∕2

This force is not of the fom F = kx
Therefore, the motion of the charge Q is oscillatory but not simple harmonic.