wHAT are the forces acting on a particle placed on a plate which is moving with an acceleration??
What do you mean by "particle"? An elementary particle or just a small mass that can be treated as a particle?
In any case, what forces do you think act?
Easiest way to describe this is to draw a picture of what's happening, then draw a free-body diagram next to it. On the free-body diagram draw all the contact forces first (ie everything that is physically touching it), second draw all the non-contact forces, which for your purposes will only be the effects of gravity.
If it's a small mass considered to be a particle..........................
then forces acting are...... contact force or electromagnetic force, weight, inertial force due to acceleration or d'alembert force to convert the problem into statics..........
Separate names with a comma.