A lift (elevator) is operated by an electric motor. It moves between the ${\text{1}}{{\text{0}}^{{\text{th}}}}$ floor and the ${{\text{2}}^{{\text{nd}}}}$ floor at a constant speed. One main energy transformation during this journey is

A.     gravitational potential energy $\to$ kinetic energy.

B.     electrical energy $\to$ kinetic energy.

C.     kinetic energy $\to$ thermal energy.

D.     electrical energy $\to$ thermal energy.

D

There is a popular misconception that a decrease in gravitational potential energy will always be associated with an increase in kinetic energy. As the lift (elevator) descends, the speed is constant and as a result, the kinetic energy of the lift (elevator) remains constant. This does, of course, lead to an interesting opportunity for discussion related to conservation of energy.