Answer
a). (4) all the same. Because the change in potential energy does not depend on the reference point. It is the change in potential energy which is same whatever may be the reference point.
b). PE at basement = $mgh=1.5\times9.8\times(-3)=-44J$
PE at attic =$mgh=1.5\times9.8\times4.5=66J$
c). Change in potential energy =$-44-66=-110J$ .i.e $110J$
Work Step by Step
a). (4) all the same. Because the change in potential energy does not depend on the reference point. It is the change in potential energy which is same whatever may be the reference point.
b). PE at basement = $mgh=1.5\times9.8\times(-3)=-44J$
PE at attic =$mgh=1.5\times9.8\times4.5=66J$
c). Change in potential energy =$-44-66=-110J$ .i.e $110J$
