Physics
Mechanical Power
Updated Oct 28, 2026
Calculate the rate of doing work or transferring energy.
What you’ll learn
Calculate the rate of doing work or transferring energy.
គណនាអានុភាពជាអត្រាកម្មន្ត ឬការផ្ទេរថាមពល។
Meaning and use
Average power is transferred energy or work divided by elapsed time. The same energy transferred faster gives greater average power. A watt is one joule per second. Power is not the same quantity as energy, even when both describe the same machine.
អានុភាពមធ្យមជាថាមពល ឬកម្មន្តចែកពេលវេលា។ ផ្ទេរថាមពលដូចគ្នាលឿនជាង ផ្ដល់អានុភាពធំជាង។ 1 W = 1 J/s។
Formulas
Average power
\[P=\frac Wt=\frac{E}{t}\]
Rearrangement
\[E=Pt\]
Symbols and units
| Symbol | Meaning | Unit or restriction |
|---|---|---|
| P | Average power, or constant power in E = Pt | watt (W) |
| W, E | Work or energy transferred | J |
| t | Elapsed time | s |
Conditions and limits
- Time must be positive.
- E = Pt uses constant power or average power over the stated interval.
- បម្លែងនាទីទៅវិនាទី បើចង់បានឯកតា W។
Worked examples
A lifting machine
A machine does 600 J of work in 3 s.
- Calculate \(P=600/3=200\) W.
200 W
ចែកកម្មន្តនឹងរយៈពេល។
A minute-long transfer
A device transfers 1200 J in 2 minutes.
- Time \(t=2\times60=120\) s.
- Power \(P=1200/120=10\) W.
10 W
ត្រូវបម្លែងពេលវេលាមុនចែក។
Common mistakes
| Instead of | Use | Why |
|---|---|---|
| Power is measured in joules. | Power is measured in watts. | Joule measures energy; watt measures energy per second. |
| 1200 J in 2 minutes gives 600 W. | It gives 10 W. | Use 120 seconds. |
Practice
Solve these before revealing the worked solutions. Include units where relevant.
សាកល្បងដោះស្រាយមុនបើកមើលចម្លើយ។ សូមបង្ហាញជំហាន និងឯកតាដែលពាក់ព័ន្ធ។
- Find power for 900 J in 30 s.
- A constant 50 W device runs for 10 s. Find energy.
- Two machines transfer the same energy; one takes half the time. Compare average power.
Answers and steps
Show solutions / បង្ហាញដំណោះស្រាយ
-
30 W
900/30 = 30.
-
500 J
50 × 10 = 500.
-
The faster machine has twice the average power.
P is inversely proportional to time for fixed energy.
Quick recap
- Power is a rate.
- Convert to seconds for watts.
- Distinguish energy from power.