Solutions:
The quantity of power consumed by a source is determined by two factors:
(i) The amount of work done by the source and
(ii) the amount of time it takes the source to do the job.
Consider the following scenario:
If a coolie A lifts a load to the top of a bus in 1 minute and a coolie B lifts a load to the roof of the same bus in 2 minutes. The job done by both coolies is identical, but the power expended by coolie A is twice that of coolie B since A completes the task faster than B.