Two cranes might lift the same load to the same shelf, doing the same work, yet one finishes in seconds and the other takes a minute. Power captures that difference: it is the rate at which energy is transferred, the joules delivered each second.
Power is the rate of doing work, or the rate of transferring energy: P = W ÷ t = ΔE ÷ t. It is measured in watts (W), where one watt is one joule per second.
Two machines race to do the same job, lifting the same load to the same shelf, so each transfers the same energy. Set how powerful each one is and start the race. The more powerful machine delivers those joules faster and finishes first. Power is the rate of energy transfer: the same energy in less time means more power.
Power tells you how quickly energy is transferred, not how much. A device rated at 2000 W is not storing 2000 J; it transfers 2000 joules every second. Always divide the energy by the time, and quote power in watts, not joules. Forgetting the time, or leaving the answer in joules, is the usual error.
A motor does 1200 J of work in 8.0 s. Calculate its power output. A second motor delivers the same 1200 J in 4.0 s; find its power.