A 12.0-kg microwave oven is pushed 8.00 m up the sloping surface of a loading ramp

The answer to this question is    physical changes are those which are perceived by our five senses. chemical changes are not perceived by our five senses.  no, physical changes does not change the identity of the substance. as far as chemical changes are concerned, they does change the identity of the substance. 
an example of physical change is water being cooled and then heated. there is no change in the tetrahedral geometry of individual water molecules. so its identity is preserved. other examples include breaking glass, cutting wood, melting ice, and magnetizing a piece of metal. 
now coming to the chemical changes, they are always accompanied by energy changes. if the energy released by the the reactants, the process is exothermic, i.e, the released energy exceeds the activation energy. conversely, if the energy is needed by the reactants to be converted into products, this process is known as endothermic.