3.5.A.1Concept
Power is the rate at which energy changes with respect to time, either by transfer into or out of a system or by conversion from one type to another within a system. Its unit is the watt: 1 W = 1 J/s.
ExampleSame work, different power1 / 3
Two students each lift an identical 10 kg box 1.5 m onto a shelf at constant speed. Student A takes 3 s and Student B takes 6 s. (a) Find the work each student does. (b) Find the power each student delivers. (c) Who has more power, and why, if the work is the same?
Try it on paper first, then reveal each step to check your work.
Step 1 — (a) The work
At constant speed each student lifts with a force equal to the weight, mg = 100 N, through 1.5 m: W = (100)(1.5) = 150 J for both.