Which quantity describes the rate at which work is done over a period of time?
Power
The quantity that describes how fast work is done — the rate of doing work over time — is Power, which is the correct answer.
Power is defined by the relation:
Power (P) = Work done (W) ÷ Time taken (t)
Its SI unit is the watt (W), where 1 watt = 1 joule per second. A larger power rating means the same amount of work is completed in less time. For example, two motors may do the identical amount of work in lifting a load, but the one that does it faster is the more powerful. Power can also be written as P = Force × velocity for a body moving in the direction of the force.
The other quantities describe different physical ideas and are not a "rate of doing work":
- Displacement is the straight-line distance and direction between a start and end point — a measure of change in position, not of work rate.
- Energy is the capacity to do work (measured in joules); it tells you how much work can be done, not how quickly.
- Force is a push or pull that can change a body's motion (measured in newtons); it is one factor in doing work but is not itself a time rate.
Hence only Power captures the notion of work done per unit time.
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