what does (ds/dt)2 (d2s/dt2) represent
ds/dt = velocity
so
(ds/dt)² = velocity²
and
d(velocity)/dt = acceleration
d (ds/dt) / dt = acceleration
d²s/dt² = acceleration
For understanding the logic:
First, go through this link:
Then,
Please try to understand the topic of differentiation as given the ncert math textbook, just the basics. Then you will be able to understand the concept used. It is highly important that you understand this so that you may get good marks.
Feel free to ask if you have any doubts.