What is Power?
Power measures how quickly work is done or energy is transferred. Two machines can do the same amount of work, but the one that finishes faster has greater power.
Power is P = W/t, measured in watts (W), where W is work done in joules and t is the time taken in seconds. One watt equals one joule per second.
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Step-by-step worked examples
A machine does 2000 J of work in 10 s. Find its power.
P = W/t = 2000/10 P = 200 W
A motor lifts a load, doing 5000 J of work in 25 s. Find its power.
P = W/t = 5000/25 P = 200 W
A sprinter does 300 J of work in 2 s. Find their power output.
P = W/t = 300/2 P = 150 W
Flashcards
Quick quiz
Q1.A device does 1000 J of work in 20 s. What is its power?
Q2.What is the SI unit of power?
Q3.If the work done stays the same but the time taken doubles, power…
Q4.1 watt is equal to which of the following?
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Common mistakes
Confusing power with energy or work. — Correct: Work/energy (J) measures total effort; power (W) measures the rate at which it happens.
Mixing units, e.g. using minutes for t instead of seconds. — Correct: Convert time to seconds before dividing, since the watt is defined per second.
Assuming power increases the longer a task takes. — Correct: For fixed work, power is inversely proportional to time — taking longer means less power.
Forgetting that power can also be found from force and velocity. — Correct: For a constant force moving something at velocity v, P = Fv is equally valid.
FAQ
What is power?
Power is the rate of doing work or transferring energy, measured in watts: P = W/t.
What is the power formula?
P = W/t, where W is work in joules and t is time in seconds, giving power in watts.
How do you calculate power?
Divide the work done by the time it took. Example: 2000 J of work in 10 s gives P = 2000/10 = 200 W.
What are examples of power?
A light bulb's wattage, a car engine's horsepower, and a person's power output while running are all everyday examples of power.