technicly yes...but partially since when u lay down (on the floor im assuming) ur hands cant go lower than ur body is, so its like doin a half of rep. and ofcourse barbell is much more convenient, and that way u will get better workout (much better) and also be able to work with higher weights.
Better off to throw that plate on your back and do pushups..............
Thats true, i agree, but the plate will bever stay stable, and cause u disscomfort.