question_answer

                  Why does a block of plastic released under water come up to the surface of water?    

Answer:

                  The density of plastic is less than that of water, so the            force of buoyancy on plastic block  will be greater than the weight of plastic block displaced, i.e.,Hence, the acceleration of plastic block will be in upward direction, and comes up to the surface of          water, Mathematically, Acceleration, a = B - W   is positive in upward direction.