Power
Power
- Two machines can do the same work but take different times. The faster energy transfer has the greater power.
- Power describes a rate, not a total amount of energy.
Compare the same work over time
same energy
more time
less powersame energy
less time
more powerDefinition
1 markWhat is meant by power?
Model answer: Work done per unit time.
Symbols
- = power (W)
- = work done or energy transferred (J)
- = time taken (s)
- One watt means one joule transferred each second: .
- For the same work, less time means greater power.
- For the same power, more time means more energy transferred.
Worked example
A lifting motor
A motor lifts a 500 N load through 12 m in 20 s. Find its useful output power.
- Useful work: .
- .
Answer
Your turn9702/21/M/J/25 Q3(a)
Define power. (9702/21/M/J/25 Q3(a))
Show worked answer
Worked answer: Work done per unit time.