Need a fast answer on calculating power (P=W/t)? Power Calculator answers with the steps beside it. You supply Work (J) and Time (s) to Power; the answer follows at once. Nothing in Power is a black box. Power suits budgeting and planning checks. No sign-up is needed for Power. The math runs on your device. Looking for energy per time or free online power calculator? Power covers both. Power shows formula, assumptions and result together. Open Power and enter your numbers.
What the defaults give
500 J of work done in 10 s is 50 W.
Power is the rate of doing work, so the same energy delivered in half the time doubles the power.
The formula
P = W ÷ t, with P in watts, W in joules and t in seconds.
One watt is one joule per second. The equation says nothing about how the energy is delivered — a 50 W motor and a 50 W lamp consume at the same rate, even though only one of them moves anything.
Worked examples
500 J in 10 s → 50 W
250 J in 10 s → 25 W
1000 J in 10 s → 100 W
500 J in 5 s → 100 W
500 J in 20 s → 25 W
Both directions are worth noticing. Doubling the work at a fixed time doubles the power, and halving the time at fixed work does exactly the same. Lifting a 50 kg crate one metre takes about 490 J; doing it in one second needs 490 W, while doing it in five seconds needs 98 W. That is why a slow lift feels easy and a fast one feels heavy even though the energy is identical.
Where this shows up
Motor ratings are mechanical output, kettle ratings are electrical input, and the two are not interchangeable without an efficiency figure. A 1,500 W kettle draws 1,500 W of electricity and delivers close to that as heat, while a 1,000 W motor might deliver 850 W at the shaft. Efficiency is output divided by input, so the missing watts leave as heat and noise.
For human effort, sustained power is a useful fitness number: a fit cyclist holds roughly 200 to 300 W for an hour, a tour rider around 400 W, and a sprint can exceed 1,000 W for a few seconds. The total energy is the same arithmetic in reverse — 300 W for an hour is 1.08 MJ, or about 258 food calories of mechanical work.
Units to keep straight
Kilowatt-hours bill electricity: 1 kWh is 3.6 MJ, so a 50 W device running for 20 hours uses 1 kWh. Horsepower is 745.7 W mechanical, which is why a 100 hp car engine is about 75 kW.
If your time is in minutes or hours, convert to seconds first. Power in watts requires seconds, and mixing units is the most common way to be out by a factor of sixty.
Frequently Asked Questions
What is 500 J in 10 seconds?
50 W. Power is work divided by time, so 500 ÷ 10 = 50 watts.
Why does the same work give different power?
Because power measures the rate, not the amount. Doing 500 J in 5 s gives 100 W; taking 20 s gives 25 W.
How do I convert minutes to seconds?
Multiply by 60 before dividing. One minute of 500 J work is 500 ÷ 60 = 8.33 W, not 500 W.
Is a watt the same as a joule?
No. A joule is an amount of energy and a watt is one joule per second. A 50 W device running for 10 s uses 500 J.
How many watts is one horsepower?
745.7 W for mechanical horsepower. A 100 hp engine is about 74.6 kW of output.
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