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 of energy to another within that system.
ExampleSame energy, different power1 / 3
Two cranes each lift an identical 500 kg load a height of 10 m. Crane A takes 25 s to complete the lift; Crane B takes only 10 s. (a) Find the energy transferred to the load–Earth system by each crane. (b) Find the average power delivered by each crane. (c) Explain why the two cranes can transfer the exact same energy, yet not deliver the same power.
Try it on paper first, then reveal each step to check your work.
Step 1 — Energy transferred (same for both)
ΔE = mgh = (500)(10)(10) = 50,000 J for both cranes — the lift itself (mass, height) is identical.