In Archimedes principle....the formula we use....there we say that wen we dip a body...the fluid exherts a force of buoyancy equal to displaced liquid....now suppose we take a metallic sphere in the first case and then a plastic sphere....then....would both the answers be the same for the two spheres or different?(Since volume of both is the same)Please explain...

it is true but the forces are different as the density of metallic sphere is more than the plastic sphere is the metallic one goes deeper than the plastic so more water is replaced by the metallic sphere.

we have to leave on the surface of the water/liquid and see how much water is replaced and not by pushing them into the water to immerse them totally inside.

the principle is when we immerce the body in a liquid the boyancy force is equal to the WEIGHT of the water repaced....

of understandin you can say that the 

FORCE <boyancy> = WEIGHT OF BODY / specific gravity....

in case of metal sphere

F<net>= W-W/p                                       W= weight of metal sphere

                                                              p= specific gravity of metal sphere

in case of plastic shere

F<net>=W-W/p                                        W= weight of plastic sphere

                                                              p=specific gravity of plastic sphere

science the volunme replaced by the bodies is same the boyancy force is also same BUT

F<net> is not same.....